That is a great pistol you've gotten your hands on. As far as using non-corrosive ammo, if you are using anything manufactured (someone has the exact date somewhere on here) in the past twenty years you will be fine.
The FMJ RN means that it is full metal jacket, round nose.
The +P and +P+ deals with the pressure the cartidge is generating. You will have to check your owners manual for the specifics regarding what your pistol will tolerate.
The only reason I can think of for varying the grain bullet you are shooting with a new pistol would be to find out which works best for you in your specific pistol. I think you are pretty much limited to 115 and 124 grain. There are guys on this board that will be able to tell you some of the better loads in each of those grains.
Have fun with your new pistol, like I said it is a great little gun. I bought the same one for my wife about two years ago and she absolutely loves it.