You're coming at a beautiful time of year here! I've lived here for a while (12 years on and off - back here now for the last 2) and I love showing people around!
Scoma's at Fisherman's Wharf is good if you want to sit down for seafood. Any of the clam chowder in a bread bowl places at Pier 39 or Fisherman's Wharf will be fun too (stand up, street food style). Union Square is good for shopping, North Beach for Italian food. Also, if you're here on a weekend check out the Ferry Building Farmer's Market on Saturday mornings (until 2 I think). There's all sorts of produce, breads, cheeses, olives, etc and it's really fun. You can also check out sfstation.com and yelp.com to find events and happenings on the weekend you'll be here. Yelp is really big out here so if you're looking for a restaurant it's always good to "Yelp it" and get some ideas!
Your hotel is near Japantown and the Fillmore District - lots of fun boutique shopping on Fillmore St - totally walkable from your hotel (I have to do the window-shopping kind, but it's still fun.) Also, lots of sushi and asian noodles in Japantown.
The buses are a great way to get around town (especially to get to Fisherman's Wharf because otherwise you pretty much have to cab, and parking is expensive!) It can be overwhelming at first to figure out the schedules if you're not used to taking public transit but the drivers are really helpful. (Also will give you a taste of the "real city") You need $2 in exact change when you get on the bus. Info on routes is at 511.org and Google Maps will give you directions using public transit also. From your hotel you can take the #47 bus to Fisherman's Wharf area - walk 4 blocks to Van Ness St and the stop is right there. You can also take the #2 on Gough St to get downtown - to the Ferry Building and the Powell St Cable Car stop. The cable cars are fun of course but the line will be really long on a nice weekend! (Best to do first thing in the morning!) Cabs are also do-able, of course - from where you are everything in the city should be less than a $15 ride.
Your hotel staff will probably also be able to point out some buses, etc. It's a great hotel but just be aware that a few blocks south & east of your hotel is the Tenderloin neighborhood - so be sure not to walk around there at night. (Not to scare you, but just be aware that if you wander over there you have to be a bit careful). I'd stay on Van Ness or Fillmore (busy, well let streets) if you're walking South. Everything north of your hotel is the ritzy part of town so you'll be fine.
Hope that's a bit of help! Have a great time!