Well, if it’s really a jungle you want, then it won’t be jag. All jungle jags are part coastal, all anything jag is part coastal.
All carpet pythons undergo ontogenetic color changes early in life. No absolute certainties, but almost certainly these bone-white colors will turn tannish/light brown in a year or two. And speaking of color changes, don’t expect to see any black and yellow baby jungles, they will look a lot like coastals as youngsters. Pics of the parents will give a clue of what you can expect, again without any guarentees.
I keep baby carpets in tubs, but they’ll outgrow them quickly and are not appropriate for adults. With appropriate hides and cover a young carpet will do fine in the 18 inch cube. Definitely add some climbing apparatus if that’s the way you decide to go.