There really is no right or wrong when it comes to tubs verses tanks, as Deb said, it more a matter of what works best for you. I'd just go with the 20, and clutter the heck out of it. In addition to crumpled paper, I have used cheap dollar store fake plants, which look nice and are cheap enough to be trashed if they get too stained up. I use tubs and racks to save space, but I have quite a few snakes. For just one or two, I would use some kind of display setup so I would have more of a chance to see them when I didn't have time to get them out. Good luck with your new friend.
Thank you very much! I am planning on many plants now, I'd just love to make it a comfortable home for him or her. I am almost uncontrollably excited. Thank you again!