Unfortunately, it can be very tricky to have a school of otos with 0 extra supplements, same as any other critter that primarily feeds on diatoms in the aquarium.
A big factor here will be how healthy of a planted tank you have. If the plants out-compete virtually all algaes, yer gonna have to supplement no matter what, even with just a few otos. On the other hand, if things are unbalanced to the point where an abundance of algae grows, the otos will be set for life. (but the tank might not be too happy)
Fortunately, 65g is huge and ~100w is more than enuff juice to grow tons of algae. You could easily have a school of 10 otos that never need to be fed, but again it all depends on tank balance and how much algae you can produce.
I like feeding my oto's, they are actually pretty fun to watch. They devour any form of squash I give them, and like pretty much any other veggies too. A quick 30 second steam in the microwave seems to make it go faster (they like it more)