In regards to SB and an effective zone defense, I would say that SB is helpful but not necessary on guards. If you have a 6 or 7 SB guard that can contest shots well, that only helps, but it is not worth training it. As for SF's it really depends. Depends on whether the other team has an inside or outside SF. Personally I would like the SB to be 8 or 9 on my SF's, in order to be safe against a possible inside attack. As for bigs... this is where it gets tricky. For my starting bigs, I would want at least 10's among both, and preferably up to 12 on at least one of them.
In regards to passing, im a real fan of the true point guard build. I like my PG to have at least 14 PA, and depending on the offense, my SG so have at minimum 12, and preferably 14 also. On the SF, it depends on his build. an offensive SF, PA should be about 11-12. A defensive SF should be about 12-13. And as far as bigs go, I think 6+ is generally a good bar. This was an issue we struggled with last season, where our best passing big was 4 PA.