A bit early to be thinking about that, still a lot of good riding to do. Actually autumn is my preferred season: less bugs, less humidity, beautiful scenery, ...
I ride through the winter also. Last two winters I've ridden the singlespeed and it's been good (didn't have a geared bike actually...). I've put together my trail bike back, around 4" of travel. It'll probably be a mix of both this coming winter.
I agree the winter is nice when everything is frozen over. It's tricky sometimes though as even in the dead of winter some areas can still thaw a bit when it's sunny, and then it's not so fun. Too much snow can be trouble too. Over 10" and you're contemplating an amazing cross-training session... Below that however it can be quite fun. I have ridden many times in deep and compacted snow, I think it's great for balance. Just don't expect to go very fast.
I'm also a big sweater, the key is clothing that wicks away moisture. I have an MTB-specific winter jacket and will wear only that and a long sleeve jersey underneath (well, not only, I have my tights and shorts also). It's usually good for 2-3 hours, as long as I don't stop (which I don't anyway). What bothers me most is the hands actually; it's really tough to find gloves that will keep you hands comfortable.