As long as your 5S is the same year or newer than your car, you should be good as far as smog goes. Also, you probably would want to look at a 95 or older 5S since they'll be OBD I rather than OBD II. Also starting in 97, the 5S use distributorless ignition with waste spark.
Mixed driving, I got about 27 MPG on my 2000 Camry I4. But that car is probably quite a bit heavier than your car and it was automatic too. If you are doing more open highway driving (doubt it though since you're in SF) your mileage might be better. Most I've ever got was about 31 MPG round trip going about 57 MPH between here and the Nevada border. I think there were about 5 stop signs the entire way there. Each way was about 140 mi.
I really don't know enough about swapping engines to tell you much more though.
Mixed driving, I got about 27 MPG on my 2000 Camry I4. But that car is probably quite a bit heavier than your car and it was automatic too. If you are doing more open highway driving (doubt it though since you're in SF) your mileage might be better. Most I've ever got was about 31 MPG round trip going about 57 MPH between here and the Nevada border. I think there were about 5 stop signs the entire way there. Each way was about 140 mi.
I really don't know enough about swapping engines to tell you much more though.