yeah that is the best way, they are going to miss a lot of the food so feed a lot at once. I've used frozen mostly, krill, brine, squid, etc. but a little cyclopeze every now and again works too.
the rubble idea is the best way to assure that they have some place to hide form the mandarin and other fish. It will provide them with a place to hide and grow, and as they get larger they will leave the pile.
you mean 46 g right? I don't think they make a 36.. and no a 250 would probably be fine on a 46, just make sure you've got fans running over the tank and the light is a few inches elevated off the waters surface at least.