I've been using ISBoxer for a couple months now and have the same background you do ( 3 boxed EQ with 3 computers, keyboard, Nostromo keypads, etc) so I agree it's overwhelming in the beginning but once you get the hang of things it all starts to make sense.

I can get you started until the more knowledgeable community members can answer what I can't or give you a better way to do it than I'm probably doing it.

First download an addon called Jamba.....this will take care of quest accepting, invites and a number of other things you mentioned. Very easy to setup and you can grab it on Curse.

When you setup ISBoxer using the wizard it automatically makes default keymaps for your characters so very little is required on your end to start playing. You can see all the default keymaps in ISBoxer in the keymap section "general" "control" "FTL DPS keys" they can be changed to whatever is better for you.

So with your main team you can simply place a spell in slot one of the action bar and when you press "1" they all cast it. So with your team smite in slot one with priest, lightening bolt in slot one with shammy's and they will cast those spells at your Pally's target everytime you press "1". That's all setup simply by using the wizard in ISBoxer. Throw heals for each character in slot 7 and when you press 7 they all cast heal on themselves, etc

As you level higher and start to add spells then you have choices to make for casting multiple spells using a single keymap. I'm currenty using only in game macros so for instance you would make a /castsequence macro for your priest and place that in the one slot and be able to cast Shadow Word: Pain followed by Smite. You have other options but at this point I think I'd just confuse you even more. Lots of good stickies on setting up macros

http://www.dual-boxing.com/threads/3...to-Multiboxing

http://www.dual-boxing.com/threads/4...tiboxing-Vol-2

Excellent video for setting up IWT

http://isboxer.com/index.php/videos/...ith-target-101

That should at least get you started