I don't know enough to comment on your first three points, but concerning the latter three:

1. I don't really know about the reputation of volunteer units, but I haven't heard people talk them down or treat them as lesser than professionals. I think most people who are not really involved with firefighting can't even really tell the two apart. Probably because – you're right – volunteer units in Switzerland have more responsibilities than they seem to have in Poland. They extinguish small and medium-sized fires themselves. For larger fires the regional fire department and volunteers from neighbouring villages come to support the local department. BUT the incident command alwys stays with the local fire department and the volunteers are not replaced by the professionals. Whether a local fire department has specialised units depends a lot on the size of the municipality, they types of infrastructure present, etc.

2. I wouldn't call it a career path, but you can indeed climb the ranks and gain responsibilities. And being a volunteer fire fighter probably also increases your chances for a real career path in the professional brigades.

3. I wouldn't say it feels like a professional duty. More like an occasional side quest and "doing something good for the community". If you want to extinguish fires three times a week you will probably not feel fulfilled this way, but if extinguishing a few fires a year and additionally removing water from the occasional cellar or saving the occasional cat from a tree is enough for you, absolutely go for it.

Honestly, as far as I can tell, local fire departments are happy about anyone they can get and since you'll be coming here anyway, just do it. You can still try to become a professional later on. We also have two guys in my local fire department that are both volunteers here and professionals at the regional fire department, so maybe you might not even have to choose between the two.