I would advise a full set of Roush springs or it'll look odd. I have Roush springs over Tokico D-spec shocks and it still sits higher at the back than Eibachs. LCAS are advisable but not essential because it's not like you're going to be struggling with the power

I don't have the adjustable PHB either because the wheels I have seem to sit fairly centrally anyway so I'd lower, fit the wheels and then see if you need one. Roush isn't a massive drop like some of the springs out there.
The V6 doesn't come with a sway bar (I think the Pony pack might but not sure) and it's always nice to have but it needs to be matched with a suitable front bar so you don't ened up with excess understeer or oversteer. For the V6, buying a pair of V8 cast-offs would be your cheapest bet (possibly paired with some poly bushings) although I don't know if you need additional brackets to fit the rear bar on the V6.
Roush springs won't wear out the stock shocks any more than they would normally but they're pogo-sticks compared to a good set of shocks. Tokico D-specs are great being adjustable so you can firm up the ride at will and are selling for $550 a set Steeda or
LMPerformance's Mustang Parts, Camaro Parts, Corvette Parts, GTO Parts, Trans Am Parts and more.).
Aftermarket LCAs come with poly bushings which being harder take out the deflection inherent in the stock rubber bushes. Harder is always better for control but the ride will be a little harsher, a little noisier perhaps. I think BMR are a good quality manufacturer for reasonable prices.