I shoot lefty. I shoot both slabsides (no forward assist or brass deflector) and modern A2 rifles.
The worst thing that has ever happened while shooting my slabsides is getting hit in the cheek or the ear with a shell casing once out of every 50 or 60 rounds. No offense, but if that's really a scary thought to you, I'm surprised you are interested in the shooting sports.
As for the A2s, with that case deflector built in, it is nearly impossible to get hit with your own empty brass. The type of stock really shouldn't matter much, because your nose should be right up near the charging handle, no matter what AR you are shooting.
I say try a "regular" AR, if possible, and see how it feels. I believe it's bad to practice with a special non-standard rifle in case you have to use a standard one some day. Better to learn how to use the real deal, IMHO.
Good luck and enjoy the new AR15, when you get it.