Personally, you are not going to like the recoil of the .357 Magnum in that small platform. At least I did not like shooting a friend of mine's. He had some .38 Special +P's that were not too bad.

Any .38 should work fine, +P or not. I have never heard of +P .357 and certainly wouldnt want to shoot one if they existed.

"What grain for practice?"
I assume that you're referring to bullet weight.

First, I suggest that, as a beginner, you do not want to start out shooting .357 Magnum cartridges. Your hand will hurt, and you will develop a severe flinch.
Yes, .38 Special cartridges will fit, and will work correctly.
No, you do not want .38 Special +P cartridges, for the same reason that you should not yet try .357 Magnum rounds.

What you want are the "softest-shooting" .38 Special rounds.
They're great for learning how to shoot, and they're OK for self-defense, too.

I strongly suggest that you find 158-grain, .38 Special, low-velocity ammunition.
Slow, heavy bullets deliver recoil that's more like a slow push than a sharp jab.
They're easy to control, and easy to learn with.

If you try to go all macho, you won't learn anything except how to miss.

Winchester White box .38 spc available at Wal Mart ...reasonable priced, soft shooting and plentiful......JJ