An important caution depends on the size of the Illithid community. Is this actually a city, or an outpost?
If it's big enough, you may find yourself up against an Elder Brain. If they have one, the mind blanks are a must, as they can sense minds constantly at range (if I recall, though I don't remember how far), can be the equivalent of a 20th level psion, but most importantly, it has telepathy that will allow almost instant response time among the other flayers and their thralls if something odd starts happening (like masses of flayers or thralls start dying for no reason).
Another point is that Mind Flayers gain great benefit from working in concert with creatures that can drain or damage stats, so bring along materials of at least Lesser Restoration, and preferably full Restoration just in case something starts mucking with your stats, like Wisdom to mess with your Will Saves, or any stats to paralyze or catatonia you, which turns you shortly into Flayer Chow (TM).
Also, remember that Mind Flayers have SR. If you use any magic against them, don't (except Dim Anchor), use it on you, or the terrain. Mess them up with low level non-resistable spells - grease the floor beneath him, hit him with Melf's Acid Arrow for continuing damage to force concentration checks if he is a level psion or sorcerer, summoned creatures with grapple, and if you can get it - Anti-Magic Field. Everything a Flayer can do except extract your brain is either Su or Sp - keep him in the field, and he's an 8 HD warrior class schlub. Even if you are in there with him, you will likely be phsyically more adept than him without magic, and you'll also be immune to magic and psionic assaults from outside the field.
Good Luck!