it sounds like you have a pretty good grasp on controlling them.. an addon i would recommend that i have come to love is Jamba, check that out. (it's specifically for multiboxers, helps with quest picking up/turning in, grouping, re-routing whispers, etc.)
i run all clients from the same wow folder
symlinking will help cut down on HDD activity, shorter load times, etc.
[Other] Winbolic Guide - Symlinking for XP

a second monitor can be really helpful, but if you're not going to really utilize it then there's no reason to waste $$. i would wager that if you do get one, you will use it though.

does peoples perception of you change the higher level you get?
from what i've seen, people get *more used* to you as you get higher level... you're always going to have the naysayers, whiners, and general assholes, and the people asking you to do something cool-- you'll find your own way to cope with that. if you respond to people positively and make a good name for yourself, then when you do get one of those assholes running around /yelling CHEATER OMG HE'S BOTTING, sometimes other people will bash him and you can just ignore it.