I'll throw in my 2 cents on this one.......
The heat is one of the biggest factors. You will get used to it......well sort of.
Skating, well I feel that it's one of the hardest parts of adjusting. Forward and backwards are relativly the same, but shuffling and moving side to side is a whole other animal!
It seems that going back and forth between ice and roller was always a non-event for me, but then I took a year off from roller and only played ice three times a week.
Now I'm back playing roller once a week, and ice twice. It takes me about 1/2 way through the first period to start feeling comfortable on my skates. I never used to have this problem, but none the less it still exist. I would imagine that if you were playing roller full time, this feeling would go away pretty quick.
Don't feel like having actual Roller goalie skates is a must to begin playing the position. A lot of guys I know, including myself, still use regular player skates with smaller wheels on them.
The weight of the puck is another factor. You will see the rebounds becoming bigger compared to ice due to the puck being lighter and not "sticking" to you as it does on ice. Shots that hit you dead in the chest and would have normaly dropped into you waiting glove are now exploding off of your c/a and landing 10-15 feet our infront of you.
Also depending on the level of play you are used to, the shots will generaly be coming in a bit faster/ harder than on ice.
Pad "sticktion" is another ongoing delehma in roller hockey. The purist would have you use your stock pads and learn to adapt your game acordingly, while other "forward" thinking goalies try to use every little trick and product to make there pads feel like they are on ice. This is a preferance, and you will have to decide for yourself on which path you take. Let me throw a little warning out there on this subject: If you decide to modify your pads, do it with actual materials such as velcro, nylon, and plastic. DO NOT try chemicals such as silicone and armor all........these may earn you a good butt kickin in the locker room!
I know that some of these had been mentioned previously, but I just wanted to throw my own twist in on things........hope you can use some of this.
Good luck,
Rick