Don't be nervous at all--quite a few are fine down to the low 20s, some down to the mid teens, some Agaves and Yucca to zone 5. The trick is to be able to keep them dry enough when they are dormant, because they are more vulnerable to rot at that time.

How is your drainage? Planting them under the eaves of the house gives some protection, or in pots under a patio cover can make them a lot easier. Or on berms of soil. There are some good succulent sellers in your area, for example, one is Succulent Gardens in Castroville, check out the Ruth Bancroft Garden in Walnut Creek and the UC Berkeley Botanical Garden, and the Gardenweb Cactus and Succulent forum, quite a few Northern Californians on there.

Here is a link that might be useful: Succulent Gardens

There are many! You need a copy of Sunset Western Garden Book which will help you with that question.

Here is a link that might be useful: High Country Gardens hardy succulent list

Don't listen to local nursery staff. They never know anything, and they always say it's too cold to grow things, even though they grow here. Zone 15 will rarely get below the upper 20s even in a cold year, but if you plan on succulents that are hardy to about 25 or 26F then you won't ever have to worry about them. Also check out Berkeley Horticultural Nursery and look online for other nurseries with large succulent assortments. And as mentioned, the Ruth Bancroft Garden in Walnut Creek is amazing, and probably gets slightly colder than you, yet grows tons of succulents without any protection. Remember, many succulents come from climates similar to ours.

Delospermas can take some frost. I am very impressed with Delopserum Nubigenum for its neat and tidy low habit, spreads reasonably fast, propagates easily and takes our wet winters. So impressed that I planted other delospermas, "Fire Spinner" seems equally impressive but hasn't done a winter yet. D. Floribunda has been more rangey. (Annies Annuals is having a 25% off sale right now, which carry several, and many other succulents)

Agaves that are reputed to be able to take wet and cold winters include Agave parryis, harvardiana, montana, scabra, americanas... I have many different agaves and so far have had good luck over just 1-2 winters. I keep the most vulnerable ones in pots. San Marcos Growers is a great online resource to look up succulent cold tolerance and plant information in general.

Sempervivums can take cold and wet, but need a bit of shade in summer.

Hardy Succulents: Tough Plants for Every Climate by Gwen Moore Kelaidis is a great book, and Timber Press has a newer book which I haven't seen yet on succulents for cold climates.

The Ruth Bancroft Garden is having their annual sale next Sat., 30% off, a good place to meet other succulent fanatics, and gleen lots of info and inspiration. I wish I could go, but have other plans.

You can create warmer microcilimates by planting trees, shrubs...

Enjoy!

Here is a link that might be useful: San Marcos Growers