Are head gaskets still a problem on the FB boxer?

Thought that was mostly an EJ engine problem?

Head gaskets is the key issue on that engine.
In any case as a long time and many model Subaru owner I wouldn't sign up for the maintenance program of a 4wd car if you don't need it. ever.
The plugs mentioned above are not too bad. The clutch is not too bad but invest in a good aftermarket one if you have to do one. Its almost a guarantee that the throw-out bearing will be the first thing to go, same as the clutch for all practical purposes. Most everything else lasts a good long time if well maintained. Make sure the tranny has correct fluid level and has been changed.