Bit out of date, but...I have a friend on bertox that runs 6 chars on 2 machines. (he runs 1 on the main comp, and 5 on the 2nd comp. I think he uses win-eq and a nostromo n-52 for switching).

the G15 (and nostromo) can be used to switch windows. using WinEQ (because it allows hotkeys for specific windows, eg ctrl alt 1, ctrl alt 2, ctrl alt 3, and with profiles you can specify that for instance, your cleric is always ctrl alt 3..) well, i used to use my g15 (a long time ago, lol) to cast spells on a char that I more or less ran headless. the macros went something like CTRL alt 3, 1, ctrl alt 1, with very short pauses in between. It works ok. For window switching, alt tabbing works, but you can't guarantee the 'tab' order with that many toons. Much easier to buy wineq (tehre might be a free equivalent, for all i know...) so you can specify the 'hotkey' for each character profile, so you can instantly get to say, your healer, irregardless of the visit-order of the windows.

I've ran a 6-man group in EQ, teh only thing that bothers me is well, you need tanking, healing, slowing, and crowd control. And things go to crap quick on multiple pulls at high levels. for me, anyway. Definitely doable. (Its difficult to say, get agro with the tank, keep tank and everyone alive with healer, slow 3-4 monsters with the slower, and try to mez adds with the bard or enc or whoever. Especially when you fight things that require slow to tank, which is most of the high-end game. None of that is impossible, I just find it absolutely exhausting.