If I were to load some light plinkers for the 500, my first choice would be TrailBoss and cast lead or the plated lead like Berry's or Rainier. With the bulky TrailBoss powder, no worries about powder position causing a strange detonation issue.

On the recoil of the big 500, when I first fired one, I was shocked. It's not brutal at all, the Ruger Alaskan 454 Casull is somewhat worse in my estimation, with more snap, less push. I haven't tried any 700 gr loads in mine, but I've pushed some of the lighter stuff, 370's and 440's up pretty warm. I chrony'd those 370 gr. loads at 1920 FPS, more than 3000 ft/lbs. energy and the recoil wasn't bad at all.