Plastic tubs are great!! I'm switching over to them now, and it makes it so much easier to maintain the correct temps and humidity. An UTH (or flexwatt) works well as long as you have a thermostat, and no, ball pythons don't need any supplemental lighting.

Let's see, 83x46x18cm roughly comes out to 32x18x7 inches, so that would be a perfect size. It might be a little too large for a 6 month - 1 year old, but yeah, as long as you put some fake plants and 2 nice secure hides in there he should be fine, and then he can grow into it as well

As far as the number of holes, it does depend on how dry your area is, as was already mentioned. Just try it out by putting whatever bedding you're going to be using in there and start making holes and see what gives you the best humidity. I put my holes in the sides of the tubs and I've been drilling them (1/8 inch or 0.31 cm bit), but I know some people solder them instead.