Re: HSH combo in strat knockoff
Both the jazz and the JB split nice, so make them push/pull pots and
you'll have gobs of good strat sounds as well as the humbuckers.
Re the middle pup, I wouldn't get staggered, as I don't see the
point. If I were building the guitar I'd be thinking about APS-2
to make sure there is a warmer, authentic strat sound available.
You didn't say what the fingerboard was or how twangy you want to
be. If you want to be loud (for instance you aren't interested in the
split tones in the hummers) then the APST-1 also may be a nice
choice.
[Disclaimer, I have experience with jazz, JB and splits but
have never tried Duncan strat pickups, just saying what I would
look for. Recognize that I'm also more into strat blues sounds than
metal].