I might be wrong, but I beleive that adults require about a 50 gal aquarium, so I guess juvenile will need a 30 gal. I might be wrong, but i'm pretty sure im not
And yes, it's better to have it alll set up and monitorred before the python arrives, u know u're ready when u are able to keep temps and humidity good for 24 hours.
And I like newspaper as bedding, easier way to go
hope i helped