I've heard of ppl putting their substrate in the oven... i kinda thought that was stupid but maybe I'm wrong. Never heard of freezing anything.
You'll want to clean everything now, then clean everything again regularly... so keep in mind, the more that's in the tank the more you'll have to clean... but since you have a large tank for a baby you should probably put a lot in there to take up the extra space for now. Definitely at least 2 hides on each side (cool/hot). Then other items for decorating to take up extra space.
Send us some pictures of your set up and your new snake when you get him!