I decided it would be worth it to pick out the centerpiece stone myself, so I visited Manini's shop on Monday. I ended up walking away with a good chunk of seiryu, some great plants, a book of glossy ada eyecandy, and a lot of helpful advice as well. He's a great guy, and his shop is amazing.
So after a good scrub, the centerpiece is in. I had to replant a few inches of plant material, but hopefully it won't make too much of a difference. Things are chugging along nicely. I wanted to be minimally invasive in placement, but i'm open to suggestions.
Going to order a few support stones soon. 2-3 sounds like it should do it.
*subs rotala for ludwigia red hybrid (SERIOUSLY, THAT'S GOT TO BE MY NEW FAVORITE PLANT)