I've dealt with 3 drymarchon species: eastern indigos, texas indigos, and black tail cribos. The easterns, as will surprise no one, always get the biggest reaction. In my experience, they have all behaved more or less the same with some slight variances between individuals. However, I have only personally kept and handled maybe 20 drymarchon specimens. Larger breeders have noted to me that texas indigos are slightly more high strung than easterns and than yellow-tail cribos are the most aggressive of the group. All that said, I am pretty confident you would get the "indigo experience" from really any of the species. In some cases, with "black phase" eastern indigos, it can actually be quite hard to tell them apart from a texas indigo. Red phase indigos however are pretty unmistakable.
I see no reason you can't use fake plants or really any decor with ball pythons. They won't care if it looks realistic or not.