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: 
A commonly quoted temperature to never exceed with warm ingredients or proofing environments is 43°C. If using an oven, cover your dough container, check oven with a thermometer beforehand, and be aware of radiated heat effects from the elements themselves.
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.