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How to best handle having thousands of DOM elements in browser

I'm working on building a sort of "word cloud" in the browser using html and javascript. The idea is to have a while bunch of words on the screen each one maybe with a different size or different color.
Issue is that I may need 100k+ words on the screen as it is a big area that will be covered. I have attempted to do this using pure html, using span elements with different styles for each word. However this approach makes the browser choke as I assume it is rendering too many DOM elements. Approaches using tables and divs were also unsuccessful.
I am wondering if I am approaching this the wrong way? I suspect there is a more performant way to do this, perhaps using canvas or svg, though these will require more work to integrate I would assume. I also want the user to be able to interact with some of the words such as deleting them or changing them. This makes the html approach seem easiest.
Any help or pointers would be appreciated!

Updating overflow without removing elements from the div?

If I used:
parentNode.removeChild( divHere );
It does work and the scroll bar for the overflow updates accordingly. If I use JS to 'divHere.style.visibily = "hidden";' well that doesn't work anymore. What I've done pretty much is create 115 divs that are in a container div and the user can select filters to show only the images they want, all the divs have a background image and are essentially just an image with a name under it.
So I have 2 questions:
1) Is there a way to update the overflow and make it not take hidden elements into consideration?
2) If 1) isn't possible than when I use removeChild to remove a div from the container, it does indeed disappear but what exactly happens to it? Does it disappear off the page because it's not added to any element on the page? So it essentially works like it's hidden? I don't have to worry about people seeing the images in some completely weird spot in some lesser used browser?
and well 3) If you have a better method of doing this it would be greatly appreciated
Thanks in advance for any help

The removeChild() method removes a specified child node of the specified element and returns the removed node as a Node object, or null if the node does not exist.
That null means that the element is now removed from your mark-up.
You should use it to not let the browser take that into consideration, as the browser will not find that element in the mark-up.
You can do it in this way as well:
$(document).remove(object_to_remove);
FInd more about it: http://api.jquery.com/remove/

I believe I may have a response for the third part of your question. That large number of divs in your containing div and the usage of filtering make me think you might want to look into using the DataTables plugin for jQuery (http://www.datatables.net/). It has some very nice features for sorting/filtering/etc. a large number of data elements and supports a variety of data sources. There are also some plugins for the plugin if the basic functionality isn't enough for you.
There is a bit of a learning curve if you want to do more complex stuff with it, and it might be tricky to get used to if you haven't worked with jQuery much (though being someone who hasn't worked with jQuery all that much due to not doing much web development, I can say that I quite like using it whenever I get the chance, although that may just be due to me enjoying learning how to do new things in programming), but I feel that if you're willing to spend the time on it you will have something much more maintainable than what you currently have.

Creating a custom web-based text editor using "span" elements - a bad idea?

I have an idea for a web application for which I would require full control over the functionality of the embedded text editors and the text editors must function exactly the same across all browsers. The standard contenteditable functionality is not sufficient to my needs on this occasion.
So I have been experimenting with various ways to implement a custom text editor. My first approach was to detect mouse clicks for caret insertion (though with no visible caret since there doesn't appear to be a way to achieve this). This worked rather well, but unfortunately there was no way to display the caret (aka flashing I-beam).
This means that my flashing caret must also be custom made. I can only think of two good ways to achieve this in a way which will be compatible across all browsers.
The first (and probably better) option would be to implement a custom layout engine in JavaScript much like Google have done with Google Docs.
The second solution (probably a lot easier) would be to encapsulate each character within its own <span> element and thus allowing the faux caret to be placed between specific characters. This does mean that there will be a LOT of span elements, but this would certainly achieve what I need whilst taking advantage of the browser layout engine. Another benefit with this approach is that I do not need to rely upon dodgy browser-specific text selection hacks.
So my question, is option #2 a really bad idea? If so, why?

First of all - do you really need to work on your own editor? There are Firepad and Etherpad with their pretty cool collaborative editing and perhaps more open source editors not based on contenteditable. It's really hard to create such editor, so it does not make sense to waste time on it.
However, if you really want to work on your own solution and you need exactly the same behaviour across all browsers, then you're doomed ;). Even if you'll avoid contenteditable there are definitely other things that can go wrong.
Anyway, the answer:
First option is very hard and time consuming at the beginning but it gives you a lot more power than the second one. E.g. having completely custom layout engine, you'll be able to implement page breaks without waiting for the CSS3's implementation (on which you will never could rely on, because you want exactly the same behaviour across all browsers). And in fact, you'll be able to bypass most of browsers' rendering differences. But, unless you've got a team of decent JS devs and few months (at least), I wouldn't even start thinking about that.
The second solution - reusing DOM is more realistic. I would perform some performance tests first, but having span per character would be easy to find out where the caret should be placed after mouse click. Without that it requires some trick... Which I don't know. You can try to check how Etherpad and Firepad (which uses Ace code editor) deal with that, but still - wrapping will be the easiest choice and at least on decent browsers it should not cause performance issues, unless you want to edit really long documents (but then you can start some optimizations).

Dynamically injecting code in Twitter Bootstrap carousel

So, I've built a responsive site with Twitter Bootstrap. The problem is that I've done this using visible-phone, visible-tablet, and visible-desktop. This means that when someone views my source code, I have whole sections that are included twice or three times, in order to get around problems with differences in span amounts, or, for instance, because a carousel on the tablet should have 2 items, while on the desktop it should have 4.
I'm wondering if I'm doing this right. Should I be injecting (or adding? Not sure of the right name) code to the DOM dynamically using Javascript, based on screen size? Or should I be editing around with my custom, very simple .php files based on screen size? I don't know, and I can't find an answer about good practice anywhere. I've tried looking at sites I like for this, but I never find a javascript script that specifically adds stuff in this situation. Given, I'm not sure what I'd be looking for.
Any pointers?

I would avoid using script to dynamically add the content; as a fellow developer that just makes it less intuitive (in my opinion) and I always aim to produce intuitive code for the chap after me.
If your requirements state that a carousel should have four items on the desktop and two on mobile, then I think your solution is completely valid.

A CSS-styleable countdown timer?

I imagined this would be super-simple, but it is eluding me so far. I would like to know how I can implement a timer that counts down to a specific date and can be styled with CSS.
Specifically, I have designed a background image/container and want to style the numbers so they are correctly positioned, sized, coloured and in the correct font.
There are a raft of JS and jQuery countdown timers, but none I have found output in a manner which is easy to target with CSS. Modifying the output strings (i.e. including div tags) only seems to break them, although my JS knowledge is not great enough to understand why (a guess, is that the scripts seem to target a certain div class and 'inject' the appropriate code. Perhaps introducing new divs screws this up?)
I guess my question would have to be... 'what is the easiest way to implement a countdown to a specific date, which can be styled with CSS?', although if you know of an existing plug in that does this, I will love you forever!

This is a very useful plugin for countdowns ... everything is written within a div and span's so you can easily style it with CSS - you could use images if you reallu needed to
http://keith-wood.name/countdown.html

I've used this: http://www.littlewebthings.com/projects/countdown/example/
And I can say it's awesome.
Unfortunately it's not in pure CSS, there are images, and the switch is not smooth.
But you can always learn how to make a beautiful countdown like that by studying how it works.
Here you can download the source code: http://www.littlewebthings.com/projects/countdown/downloads/lwtCountdown-php.zip
Hope it helps.