I'm newish to Monstera, but this is what I'd do:
First, repot. I would probably not divide it, I like the fuller look of having several in a pot. Use a good quality, fast draining soil and a pot with lots of drainage holes.
Monstera are giant vines. If they don't have a tropical tree to go up, they tend to start going sideways pretty quickly. If you want a more upright look, I'd add a very sturdy support post and start training them to a more upward growth habit.
The damage to old leaves is cosmetic, I'd just leave them alone. Eventually they'll drop off. The new growth looks healthy. I think it looks very good considering the conditions you found it in!
