Hey this is right up my alley!
I spent a couple years "working" as a volunteer EMT. The service I worked for was an all volunteer service in a very rural area. We received a small stipend paid per call. We responded from home and would have a day shift and a night shift during the week. Weekends were 24 hour shifts for us. Call volume was approximately 500 per year for that service.
There was a good sense of camaraderie, and a lot of the people I worked with had been doing it for decades. I got my feet wet, which was what I wanted to do, and ultimately decided to jump headfirst into the field. I've been a career firefighter in a large metro area for the last 7 years now.
I think you will likely just have to give it a go to get a true representation of what it's like. Everywhere is a little (or a lot) different, even when you're comparing departments in my metro area.
I also spent some time as a volunteer for a combination department when I got out of the academy. It was fine. I rode as additional manpower on the truck, and for that small department, any extra set of hands is a bonus.
Staffing for services that use volunteers is always tough, as well as retaining volunteers. I'm sure they would be fairly accommodating to get the help. Have fun with it, learn from the guys who have been doing it a while, the guys who do it as a career, and be safe at it.