Your entrepreneurism is good although you will very likely need a state DNR licence to sell sport fish and probably even bait fish since the state considers those fish their fish/wildlife or property of the commonwealth of PA. PA might have an aquaculture society where the laws are stated. If not then check the DNR website for regulations about selling sport fish even those raised privately.
One could get bluegills to spawn in a kids wading pool so it doesn't take much space and depth for them to spawn. However growing - raising enough of the fry to 3"-4" to eventually sell will be challenging. Growing out fry could be done using one of two basic methods. 1. Growing them on phytoplankton then zooplankton, then larger macoinvertebrates or 2. essentially on artificial feeds - first powder then gradually larger sized pellets as the bluegill grow larger. Or some combination of both methods.
There is a pretty good 'book' that describes this process: "Sunfish Culture Guide" by J.E.Morris, C.C. Mischke, & D.L. Garling. Publisher North Central Regional Aquaculture Center, 2002. NCRAC Culture Series 102. 91pp.
IMO the governmental "hoops" that you will have to 'jump through' to do this legally will probably not be worth the expense and small amount of benefit that you will receive from this idea if it is done on a small scale. Discouraging - however it is a good idea. Thank the state government for making your plan a lot more difficult.
See these:
http://extension.missouri.edu/p/G9473 http://www.ncrac.org/oldfiles/NR/rdonlyres/FEA76957-084E-4B44-9432-9028D7450C31/0/Sunfish12303.pdfSunfish Culture Guide
http://www.ncrac.org/oldfiles/NR/rdonlyr...ish_Culture.pdf 
