Yes! Embarcadero Center has many surrounding garages, and Harborview will help with validation ($2 for 4 hours at each parking garage, though they recommend #3). There is also ample street parking, as we're getting married on a Sunday (free meters!). However, because we'll be pouring free drinks for at least 2 hours, MUNI, BART, and ridesharing are probably better ideas.
San Francisco has a plethora of nearby hotels, and we're literally next door to the Hyatt Regency, if that suits your fancy. This is also an AirBnB city, so that's always an option as well.
As soon as you can. By X, 2019 would be preferable as we need to do seating arrangements.
We may set up a small registry in due time, but for now there is no registry. We are mainly doing our house purchases on our own and asking for help in putting on an expensive day in the City.