Learning with ice-skating skills?

Hello! I've been thinking about getting some roller skates to skate around campus. I've never tried roller skating before, hoever I've been ice-skating and roller-blading (?) for 17 years so I have a few questions:

1. How different is roller skating from ice-skating? Technique wise at least.
2. Is learning gonna be easier for me since I already know how to skate on blades?
3. This is probably a very stupid question but how important is a helmet as a begginer? That's all, thank you for any advice!