To start I would definitely split the sag into individual plantlets and then spread them over the area I wanted to carpet. It would look nicer and spread faster.
I'd probably put something bushy in the back right corner, maybe a hygrophila like wisteria or polysperma. That or spread the mayaca so it covers that gap a bit. Having the wood on the diagnal really pulls my eye to the top right so having it naked is quite jarring.
I kind of want something on the bottom left of the wood as well, to add a bit more interest to that area. Maybe a small anubias on the wood or a red tiger lotus in front of it if theres enough space.