I live and work in the San Francisco Bay Area which is widely known as being progressive and LGBT friendly. The community is definitely very accepting and friendly towards the LGB part of the community , but I think it is still hit or miss for transgenders. We did make the news awhile ago for the murder of Gwen Araujo in Newark, CA (part of the Bay Area). More recently, transgender students at Chabot College in Hayward, CA (part of the Bay Area too) got attacked for using gender neutral bathrooms!
Maybe you don't have to flip your personality at work. People will think everything else before they think you are trans. The uniform for men and women are the same. Whether male or female, you probably won't be allowed to wear jewelery for safety reason. You could probably get away with doing feminine things like plucking your eyebrows, style your hair, light makeup, and painting your nails (guys probably won't notice clear mascara, wetlining, and clear nail polish). If you find the right colors, you could probably even use foundation or a tinted moisturizer/sunscreen, blush, and lipstick, but girls usually do minimal to no makeup at work. It just gets messy. I would probably avoid eyeliner, eye shadow, and highlighting/contouring. Go for a natural look. People aren't going to see you wearing panties and a bra underneath (unless it is the ugly gray t shirt Rural/Metro was trying to push nation wide). EMTs use the bathroom wherever they want. When you are out in the field, nobody is going to care if you use the womens bathroom. You'll probably use the bathroom at Starbucks and gas stations a lot. You don't have to be a total boy at work. You'd be surprised with what you can get away with.
Your co-workers that you see everyday might incorrectly gender you, but maybe your patients and the public won't. Like I said, you and your co-workers will see each other frequently. The changes are so slow that you will probably have a hard time seeing the changes. You and your co-workers might see you as a boy even if you look like a total girl. People who never see you or are meeting you for the first time will see a girl though even if you are presenting as male. If your division is large enough, maybe only a few of them will think you are a boy, but the majority will see the girl you are.