Much the same as mine ( http://grahampatterson.home.comcast..../darkroom.html ), though I had the building and just had to insulate and panel it.
I find an electric kettle is more than adequate for warming up solutions. A litre or two of near boiling water goes a long way. I have a stainless steel jug that does a good job when stood in a bath of hot water.
Having a Jobo for film work takes care of a lot the temperature issues. I also have a small space heater that can stabilize the temperature in the building in an hour or so. Not that it gets much below freezing in this part of California.
Note about electric heat sources - watch your total wattage if you are using an extension or distribution block on the end of an extension. An RCD/GFCI device in the line would be wise as well.