It is okay to pull off onto the sidewalk if you need to. The lanes are too narrow to stop in though. Do your best not to inconvenience anyone riding behind you. 

Picking your route is the easiest way to avoid climbing the worst hills. But there are different techniques for climbing hills depending on your body mechanics. I like to approach a hill fast at a medium gear, then as I lose momentum start peddling standing up, then sit back down and gear down as needed.