Question: During wintertime it is often cold enough in my apartment that proofing takes much longer than in summer. I'd like to use my oven to create a warmer environment, in which the dough would rise faster. I can go 30-50 degrees celsius, the question is what temperature is safe and at what temperature will I actually start baking the dough. Is 50 degrees celsius still ok or not?

Answer: 
In the winter, I usually get fine results proofing in a bowl with a second bowl inverted on top of it, and then putting the whole thing in the oven, turned off, and just the light on. The light bulb usually produces enough heat to keep the inside of my oven at about 90˚F (32˚C?), and that gives me a good rise.
I use the pull-out warming tray on my oven set on its lowest temperature. I've never actually checked the temperature, but its rather cool. I can easily touch the bottom of the drawer without any discomfort.