Thank you! I am not used to so many choices. Here it is more like "here are your 5 trainers worth dealing with, they've all been to the Olympics! They cost $X, pick one within 100km of you." The idea of having a lot to choose from is all new and pretty exciting. It's especially nice because my horse was trained very - I don't even know what to call it - softly? and does not respond well to 'my way or the highway' riders/trainers. Finding someone who suits both of us is definitely the priority.
Oy, like they said the Bay area is huge! If you are planning on going farther south there a few dressage barns. There is an FEI trainer named Joan Williams in Santa cruz which is a bit far south but still doable. If you are looking to go farther north I would begin looking in the portola valley/ woodside area- there are so many different barns in this area you can take a look at a few. Welcome to the Bay =)
Based on your original requests, I would recommend checking out Christiane Noelting's (Vacaville). The main barn is probably between 20-25 horses and they are one of the few places with regularly irrigated pasture and turnouts. You also might contact Flying Cloud Farm (Petaluma) as I believe they have pastures and turnouts, but you would have to inquire to be sure. I agree with what mbm said about various different trainers with different accomplishments, education, communication abilities, and training styles. Best way is to create a short list and observe some of the lessons from the instructors. Facilities with turnouts, especially with fresh grass, will be more of a challenge to find. Smaller facilities (such as around 20 horses) are around, but can be a little harder to find or get into. Some areas with multiple "clusters" of options in close proximity to each other will be Walnut Creek, Martinez, Livermore, Pleasanton, and Petaluma. You can also find some in Marin, Sonoma, Santa Cruz, and the peninsula/Woodside areas. Best of luck!
Check out Tracey Hill-Mores in Concord (www.tracey-hill.com). That is east of the bay area, but it is on the Bart line. She is an accomplished trainer and rider and has trained with some of the best. She is very sensitive to the needs of the individual horse and rider. Being committed to developing oneself and one's horse is an intense journey. Tracey is a good person with whom to be on that journey. I wish I were close enough to train with her.