Congrats on the new revolver.
I have (very) limited experience in ammo for .38, so the only comment I can add regarding selection is that a box of Mag Tech LRN 158 gr I shot once was pretty smokey.
But as the guys above said, these days I guess you buy what you can. I wasn't aware the prices of .38 had skyrocketed recently ,until I had a look at ammoseek just now. Wow. I bought a couple boxes of S&B 148 gr wadcutters last fall, for LCR practice ammo to my Federal Gold Medal Match 148 gr WCs, and am glad I got it.
Good luck with the new gun. I lust after a GP100, and look at them longingly every time I'm at my LGS.