I think there's a fair amount of instruction, I'd only consider doing the whole thing over there if I had a lot of time to be there.. otherwise it might be the whole vacation. The half and half situation seems like a slam dunk to me. Do the mundane stuff at home, then do the open water part on the reef. That's what I'm doing, I think, before I go anywhere warm next time. The last time I looked into this, I checked out the Dive Shop, Adventures in Scuba, and Aquasport. Aquasport had the most reasonable rates. I got all my gear from them too, they had the nicest stuff at the lowest prices. I'm kind of annoyed though, my mask and snorkel and fins have been to far more tropical places than I've ever been to because my friends keep asking to borrow them.
Sheesh, cheapskates who don't buy their own.
Anyhow, I digress. I highly recommend Aquasport, they are in Marda Loop here in town, here's their website:
http://www.aquasportscuba.com/