Welcome to airsoft.
I will warn you if you get into it its as addictive as crack and just as expensive.
Cant comment on the RM4 I have never used one PT247 above is always raving about it and most importantly actually owns one so I would listen to his advice. Main thing is try it out with a rental for a few games then buy the one you want most, listen to advice but in the end its your money your choice. It isnt cheap especially when the wife starts threatening to leave because you spend all your time playing with your weapon not her.