Johnny,
Hi.
I would not use the O3 with a 400 gm undersuit....you might get away with a 200gm just about but really neo suits are mor suited to thermals (PBB or Xerotherms).
Most neo suits are more hardwearing than membrane for wreck diving. I've had a couple of buddies tear a membrane suit but never seen a buddy tear a neo suit.
A good price? The only place to buy an o3 is direct from the manufacturer!
So far I have not seen an O3 suit that doesn't have a zip cover.
You'll have to speak to O3 about rock boots and socks although I think you're right.
Good luck
