I've grown and grafted Avocado trees in both Northern and Southern California. Hass, Reed, and many other good types will fruit well in Redwood City and virtually all of the Bay Area.
The only areas that can't grow Avocados are the Sierras. It's even possible to grow them in Humboldt:
What time do they start showing flowers? I want to plant a few here in SoCal but I'm at around 3k elevation and we get an annual March snowstorm that likes to kill off any plant that start to show early.
They usually flower in Spring, whenever that is for you. It's cultivar and temperature dependent. Some varieties like Carmen will even flower multiple times a year (though Carmen isn't one of the more cold hardy types). Bonny Doon is a good cultivar to consider if you get some mild frost each year. If you go below 20 degrees, though, you'd need to protect the tree during the cold snap.
Yeah, that can be a separate issue with any fruit tree. There are a bunch of options, but it depends on how much effort you want to put in. (Though all the options are worth it compared to buying fruit from the store.)
Stanford has avocado trees in the quad, IIRC. Redwood City should work just as well. I need to get my hands on the Gem variety due to 100+ extended summer heat in my neck of the woods. Even then, the leaves might burn without a larger shade tree nearby.
GEM isn't worth growing -- it's not that good of a fruit. Hass does just fine even in high heat. Just plant the tree in a spot that gets some afternoon shade.
