Aloha! Welcome to the board!
Regarding round balls in a fast twist barrel: I was taught the following phrase, “Load ‘em light, and patch ‘em tight!” I take that to mean light powder charges, and a tight fit in the bore. YMMV.
If you try the Lee R.E.A.L. bullets, a few basics seem to hold true for most shooters. Get you off to a good start, anyway…
-cast from pure lead, for ease in starting the bullet down the bore
-light powder charges- don’t push them too fast, or you can strip out the driving bands
-many report a felt wad over the powder/under the bullet improves accuracy
Round balls are probably as widely available as anything, and it’s easy to experiment with different patch thicknesses. For budget plinking, round balls are probably the place to start.
Welcome (back) to the addiction!