I use AllData DIY ($25/year subscription) for most of my repairs. If I can't find it there, there are some good how-to's on the net for some things. I mostly just dig in and figure it out if it's not listed in the AllData DIY or I can't find it on the net. As the Boxster ages, there will be more and more how-to pages posted so they will be easier to find. You can just about re-build the 928 from all of the great pages on the internet since it's much older so be on the lookout for more Boxster stuff.
I don't have the FSMs for the Boxster. If they are anything like the the ones for the 928 they definitely are not worth the $500-$600 for the printed set. The 928 manuals, even though they are 9 volumes, are written for mechanics and assume you already know a lot of things.
Usually, if I can't find it at AllData or on the internet, I can post a question here and someone has BTDT and knows where to go.