Wetpup, I have been to Chuuk six times now and I would say that going all that way from Australia for only one week is not a wise expenditure of money. As the largest cost is the airfare to get there, staying longer is not that much in real terms. Since we get four weeks annual leave, lack of holidays should not be a reason to only go for a week.
I would say that a minimum of two weeks is required. I have done Chuuk liveaboard and land based and believe that land based is best. The cost for one week on a liveaboard (with airfare) is similar to staying for three weeks on land. The advantage is that you are only doing two dives a day instead of four (safer), you will do more dives and do more wrecks (the liveaboards tend to stay on one wreck for multiple dives).
Again, I would stay at Blue Lagoon as they have more boats, closer to the wrecks and are far more flexible in their diving. As to doing a course there, do it here before you go, that way you will enjoy better all the dives. The San Francisco Maru is an easy dive so long as you are good on air and a competent diver.
Yes, the wrecks are breaking up, but the wreck that was leaking aviation fuel stopped many years ago and is now diveable. The oil leaking seems to have not got worse in the almost 25 years since I first went there. In any case, the tankers are empty and any fuel is only coming from the few oil powered ships that actually had a significant amount of fuel in their tanks when they sank (most had little fuel due to Japan's dire state in 1944).
For more information about Chuuk and the wrecks see my web site:
Michael McFadyen's Scuba Diving Web Site