A block heater makes starting much easier, so I would definitely get one if I were you. I always plug it in for at least a half hour if it is freezing, and up to two hours if well below zero. I am sure that someone makes a hydraulic heater, but I am not aware of who does.
Once started, the colder the temperature, the longer I let the tractor warm up, but not more than 15 minutes in really cold weather, unless I get busy and forget.
In terms of fuel, the best thing to do in the winter is to use #1 diesel fuel which has a cloud point of -40F. I wouldn't be attempting to start my tractor at colder temperatures than that, I will wait out the cold. In our area, which can get to -40F, they sell what they call "winter diesel" which is a blend of #1 and #2 diesel. The problem is what is the blend proportions? #2 diesel has a cloud point of +40F whereas #1 has a cloud point of -40F - big difference. I have a simple solution - use # 1 in winter. There is a problem with #1. It is a poor lubricant, thus you need to use a diesel additive with #1. #2 has excellent lubricating qualities, so little if any diesel additive is needed.