Finally, my first 360 and goals for it! I'll be asking a lot of questions.

Not sure I follow you here. I could get valves with oversized stems and make them work with some work on the existing valve guides ? Or I could re use my old valves and have new guides installed?
Yes & yes, are your stock valve stems in good shape? Most often the intakes are re-usable,but the exhaust is a 50/50 bet at best. If you are staying with an OE design valve,
( i.e. not stainless or oversize dia. heads), they are usually available in .005"-.010"& .015" o/s stems for popular engines. the guides are simply reamed & honed to this o/s
dimension. If you have new guides installed, you can install any std. stem valves in them, performance & bigger than stock head dia. are now an option. But you will need the
seats cut/touched up either way, just trying to lap 'em ain't gonna cut it.