Yes you can get better battery life with the right roms.
Most of the roms remove the bloat, clean rom is really nice and smooth.
You can damage the phone but just read/read and read some more. Also dont be afraid to ask questions, even the experienced ask questions.
Check out this video it is by far the best video on how to root and well explained.
And just my 2 cents when you do root install clockwork mod recovery. Seems to be more stable than the other one (the video will explain those).