BG will feed train themselves very quickly. I've found that if I cage one or two BG with the RES during pellet training the RES will catch on a bit quicker than they will otherwise.
The difficulty in pellet training RES is getting them to figure out that pellets are food. I mix chopped fish/nightcrawlers/bugs/liver/etc with hydrated pellets to get them started.
Once they figure it out you can phase meat out of the mix over a week or so, then over the next week you can reduce the amount of hydration until you're feeding only dry pellets. You'll never get all of the RES to eat pellets no matter how hard you try. If you get 80% on pellets you've done well.
I've never started with more than 50, so can't offer good advice on how many will fit in your cage without being crowded, but my gut says 200 3"-4" inch is probably too many.
I think you'll have a very hard time getting their attention if you try this without putting the RES in a cage.