Tip #1, don't call it "san fran", or "frisco", or any other name people think is cute. It's either "San Francisco", or "The City".
As far as hills, don't worry about it. Sure there are plenty of hills, but nothing that you can't mash up for a few blocks or find a way around. It's definitely worth having a bike, but it could be worth just renting a road bike for the week (if flying your bike out is going to be a hassle).
The Tenderloin and the surrounding area all the way down Market is relatively flat. That area is sort of in a small valley surrounded by Nob Hill and Russian Hill to the North, Telegraph Hill to the North East, Mt. Davidson and Sutro to the South West, Bernal Heights to the South East, etc...