My husband chose a sea hibiscus from all the plants at Schley's bonsai in Deland yesterday. It's a large plant with a thick trunk that's ready to be potted but Jason gave ideas to create a new apex and air layer...His ideas were oriented towards turning it into a shohin and making the leaves miniature which isn't difficult to do. Shohin is something I expressed an interest in but my husband isn't interested in shohin and will let the leaves stay big. His tree is older than yours with a fairly large trunk base...(they air layered if from their own stock) and it has thick branches. He suggested removing a large branch and creating a new apex. I think it all freaked my husband out who doesn't have the time to read like I do. The thought of redesigning it isn't something he's ready to do. He's working more than full time and is learning bonsai in between doing a million other thing and managing a lot, so he'll move it into a training pot for now and make decisions on what to do with it later.
I hope someone here with miles more to offer than me will offer suggestions. I'd like to see how it goes for you. The flower on this is stunning btw, in case you haven't seen one in bloom.
Good luck with it! We'll we watching to see how you do with yours.