I have both of these in my planted 75
the sen will probably get a foot but mine is an albino and possibly a short body and he maxed out at 7"
the endli I would worry about however
they can get to be 29", but you'd have to be getting a wild caught one to expect those sizes, however, even with captive breed endli I still find that they get to be at least 15" or so, sometimes even more if feeding and space permits
My guy is 15" and I sometimes look at him and wonder why? my 75 is the same width as your tank but its 4 feet long, which I think will make a difference with a fish that gets to be 16" in length. I have also noticed that endli's are no where near as flexible as sens, meaning that the main problem I have with my endli is just making sure he has hide spots that he can get into and out of. And of course, your fish will probably pick the smallest and most obnoxious of little holes to hide itself, because thats what my guy does and then he takes a bit to turn around and get out. Just be warned that the endli may need to go when it becomes bigger
I will say though, I've never seen people keep bichirs and frogs together, only people feeding frogs to bichirs :P
as far as plants go, I find that anything on the driftwood works rather well, and anything that gets nice big roots is equally pleasant. I've seen bichirs with swords and apongetons, and I keep mine with those as well. I also keep some banana plants and red tiger lotus with my bichirs no problem at all. In fact, the only plant I have been having difficulty with keeping planted in this tank are my stem plants, although once they get rooted I'm pretty sure this won't be an issue. My stems are hygrophilia corymbosa, Ludwigia glandulosa, Ludwigia Repens, and Rotala Macaranda, but these getting uprooted I also attribute to the other fish I have in the tank and just the fact that I am not the greatest when it comes to planting stems lol
also, dwarf hairgrass, I'll let you know how that goes for me, but its been a pain in the ass to plant. And I also keep red root floaters and amazon frogbit floating at the top, which I believe makes bichirs more comfortable since they come from areas with dense vegetation.
bichirs and plants can be done, it might take a little longer but once plants get established you should be totally fine