If you buy your whole viv set up now that you would like to keep the snake in as an adult then you could buy a small plastic (12 - 15 ") container then place that into the large viv which has the right size heat pad for that viv. Then position the small plastic container half onto the heat pad.
This way you get to get everything in on shot and not wasting time by getting 3 - 4 different viv's.
Here is a picture of my set up at the moment. It has my young corn in a small plastic container about 13" long and about 6 - 7" wide, my semi adult corn shares the large viv. I wouldn’t recommend putting another snake in the viv though as it may cause stress (just temporary until I move). Both snakes are feeding very well so I know they are ok.
For hides I use the cardboard roles left over from a toilet role, I cut them in half and they make great hides
That’s for the younger corns.
Wait for the snake to get as thick as your pinkie before you put her/him into the larger viv.
Have fun selecting your corn, there are tons of morphs.
Sorry if i repeated somethings of other peoples advice ( Didnt read all of the topic)