feeding and hide question

im planning to get a mexican black kingsnake very soon. i was wondering, however, about feeding:

i know i'll ask the breeder what its been fed/how much to feed it, but when will i know when to go up a size? and when i DO go up in size, how much would i have to feed it then? i guess the best answer would be for any snake age, though i have a feeling i'll end up with a hatchling/fairly young snake

also, i have a little plastic container thing that i think would be a good hide. the only problem is, its transparent. i was wondering if painting it over or something would be a good idea. im planning on making it a moist hide

This answer is late, but it's really just your best judgment. The prey should be no larger than 1x - 1.5x the girth of your snake at the largest point. It should take your snake a minute to get it down. If your snake seems to swallow it very fast or is looking for more right away it might be time to move up a size.

I would have two dry hides that are opaque, and then the moist hide can be transparent if you want. I don't think a king snake should really need a moist hide though unless you have very low humidity in your home/area. I am not a king snake expert however.