Several things to consider with the conditions you presently have.
1. It probably is several degrees warmer in your shop than the outside temperature. My garage is not well insulated and I have a fiberglass door that is not insulated at all. It still is consistently 10 to 15 degrees warmer than the outside temp. It isn't difficult to raise the garage temp to above 50 and I seem to work much better then. I also think the products work better.
2. The paint on the vehicle may take some time to warm up if it has been exposed to the lower outside temperature for some time. The air changes temp pretty quickly, the metal doesn't.
3. If I'm washing, I use warm water. I also have my products inside where they are warm when I take them to the garage. Product temperature has never been a problem doing it that way.
4. If you use a supplemental heater, (I do), be sure to have adequate ventilation and consider the fact that the heater will probably have an open flame. Your regular heat probably has an open flame so flammable material shouldn't be any special problem.
Obviously, you need to be aware of carbon monoxide, but you also need to remember that the combustion heater will consume quite a bit of oxygen from the inside air. That's not a good thing either.
I run my heater about 20 minutes with the passageway door open about 6 inches, then close it and turn off the heater. If I need to run the heater again, I open the door again.
Charles