I occasionally multi-box raid (I don't count LFR as actual raiding, but I 3-5 box LFR every week).

Here's the thing that you won't really understand until you do it: Playing a single character in DS or any other raid isn't that hard. We tend to make it harder than it really is. The special challenge that you face as a multi-boxer is the randomness of playing with others. Generally for heroics and elsewhere I find multi-boxing alone quite relaxing, but once you introduce at least 1 other person can dramatically increase your stress because unexpected things start to happen. So, as a starting point, I would work on raiding with 1 toon, and then as opportunities open up you can try adding more.

Also, I fully agree with Apps above. When you multi-box in a guild raid, nobody wins. It's a short path to drama.