Blue:
Where you stay in SF will depend on your budget as there is a wide range of prices and hotels. Regarding the weather, March the temperatures should be in the mid to upper 50's, possibly low 60's. Your biggest concern will be whether or not it rains. No way to forecast, but March is part of the rainy season here.
As for what to see, you can take the Cable Cars near Union Square, go to Fisherman's Wharf, see the Golden Gate Bridge where the San Francisco Bay meets the Pacific Ocean, take a boat tour of the Bay and stop off at Alcatraz, go to Pier 39. These are but a few things to do. It is a beautiful City with undulating hills surrounded by the Ocean and Bay. There are many tour buses with different packages daily, so you could choose your destinations once you got here.