Hi All

I'm new to electric rc's and have a few questions. I just bought a Hobbico Profisherman. I've read what info is available on the motor but there are huge gaps that I hope someone can fill in for me.
1) Can someone tell me the voltage of 1 NiMh, 1 Li, 1Lipoly cell?
2) Can someone tell me a little more a "mAh", what does it meant and what is it's relevence?
3) The prop that comes with the boat is a 1.25"X2.01" That seems kind of big to me.
4) When I upgrade the motor, will I need to get a new esc?

Any help would be appreciated. Even if someone has a good link to "need to know" info for beginers.