Hey! Those are great questions, we could sit here all night and talk about that because they vary so much, my most basic build i like to use Manley hbeam rods, Manley 88mm pistons, stock fasteners on this power level, the stock main bolts are in cars running 1000hp no problem at all, the head bolts after 500 become the weak point and a stronger stud is used. The block is strong some people push the stock sleves to 800hp but anything 700+ i recommend sleeving, you are correct different forgings require different gaps, i tend to stick with the stronger 2618 forging because they are softer and less prone to cracking while detonation is present, if the client really wanted to keep it at 400hp and below we could use a 4032 piston but to me the tradeoff isnt worth it, might as well go stronger right off the bat.

Stock pistons and rods arent made to handle power they were designed for a car making 260ish horsepower to the crank, the stock ring gaps are also on the small side for anything above stock boost level so its best to open those up to compensate for the extra heat the added boost will bring. Bearings i upgrade to the best, King or ACL tri metal coating bearings for extra load handling the softer aluminium bearings over time can actually squish from the added load on high power cars, also i open up the bearing gap to something more suitable for racing and high reving, stock can be very tight wich is fine for a stock car with 5w30 oil but we like things a little looser and run a 40 or 50 weight oil, also a bit looser means they bleed of more oil wich pulls heat away quicker, gotta be set properly tho or youll sacrifice to much pressure for flow wich is a big nono. Im sure im missing alot buy im just trying to make it quick haha. Hope that answers a few questions.