Roller hockey pads are lighter and made of lesser materials. Ice pads are heavier to accept the speed of the puck. Do not use roller for ice, it's ok to use ice for roller.
Preferably, I think the best way to start is to play ice hockey 1st, and then roller hockey 2nd. The reason I say this is because I know a guy who learned to skate on roller blades 1st, and he had a heckuva time learning how to stop playing ice hocke...
I agree with some answers. If you want to be a goalie, be one ! If you hesitate, then maybe it's not what you really want to do. Goalie equipment costs a lot, and it's also really a state of mind. So you better be sure. I've been a goalie for two yea...