1) Start small. A team of 5 hunters. Simple to control, same class, dwarves.
2) Start them up on Sargeras, since that's where all the alliance multiboxers are?
3) Get subscription to this ISBoxer thing and spend a week or so setting it up (based on what I saw it's insanely complex)
4) Get Jamba addon and figure that one out. Are there any good tutorials for it anywhere? I would love something like MiRai's ISBoxer series.
5) Consider using LazyMacros for 1 button DPS and only manage CDs - is it something Multiboxers do? Will it be effective?
First of all! welcome! always nice to see new multiboxers!

1. Indeed starting with 5 toons of the same class is easy to learn everything! hunters will full fill your desires of multiboxing.
2. since i'm europe i dont know, but there's a post of the different realms where multiboxers play.
3. you can get a 7 day trial for using ISboxer, and you won't be needing them all to set things up! just follow the walktrough to make your own team on ISboxer.com. Lax made the setup quit easy for new users!
4. Jamba is just a download and use addon when you have setup your ISboxer. Ebony is the owner now of the addon, and doing a good job for updating and improving it.
5. Lazymacro's is the most simple way to start multiboxing. it basicly does things you can also do with ISboxer, but a bit more setup is needed then.

I hope you enjoy multiboxing!