I'd done about 170 dive when I went to Truk and did GUE fundies about 6 months before, although had been diving a twinset about 6 months before that. I wouldn't worry about any advanced deco (I.e. O2) and just build in some more time in the water. It's warm, and on a lot of the wrecks you still have something interesting to look at up to 5-10m.
The buoyancy and trim skills learned on fundies will set you up well for some of the guided penetration dives you should get the opportunity to do, assuming you don't mind popping into a wreck for 10-15 minutes without seeing any natural light The guides know the wrecks like the back of their hand, but there's a big dollop of trust! Some of the holes are pretty tight too, so not sure I would have fancied an extra stage!
A big torch is pretty much essential, along with a decent computer that's not going to hammer you for deco when your not at exactly 6m (I.e. Suunto). I think my Suunto backup was bent after 3-4 dives and was eventually switched to gauge mode
I did a few days diving from the Blue Lagoon and then spent a week on Odyssey, and there were a few people diving a single 15 but I think a twinset is really needed to get the most from your trip.
You'll have a great time. The diving is fantastic, although very rust based with a lack of any really big wildlife!
ps: the GUE approach is a little prescriptive if you want to to progress down their technical courses, but the skills learned on fundies can be applied to any diving you do afterward, with or without GUE. It's a hard course, with a pretty high bar (unlike anything you might have done with PADI) but we'll worth it with the potential to make you a much more proficient diver.
pps: oh, and Nitrox is a given - 32% good for most dives with 28 or air for the deeper ones!