Kuhlis aren't too bad on bioload, and hardly take up any space - maybe four or so?
Gravel vacs aren't a problem IME - mine tend to hide right out of the way when the vac is in, and if i get the occasional one that doesn't want to get out of the way, I just give it a gentle nudge with the vac, it soon runs off! I have yet to suck any up.....
As for the gravel bed, not really a problem - they won't dig into gravel (I have sand, and they don't even dig into that too much), so I'd say whatever you have already should be fine. That said, they'd probably like you a lot more if you had sand instead of gravel?
Khuli's will find the darkest and most secluded cave or rock outcrop or anythng that they can hide so don't worry. And if you get too close, they will run away and not just stay they to get sucked up.
i mean, what if they're in under the gravel and i can't see them? i dig deep when doing gravel vacs, so what if a kuhli gets caught between my rapid thrusts of the vac and the gravel? also, what happens if i never gravel vac?
if a khuli loach gets sucked up it will do it no harm, probably just stress it out a bit, but they should have anough power to swim away, theyre very fast!
they wont bury themselves completely in the gravel....
if you never gravel vac then you the bits of waste that wander down between the bits of gravel will just decay and make your tank smell and look bad. also will effect water chemistry