About the temperature.... don't worry about it too much.

Get your developer to a desired temperature, say 20C. Pour it into a canister and do your processing. In 5 to 10 minutes it takes in the tank, it won't rise that much, assuming you are doing this in human comfortable, air-conditioned environment. I tested this myself and I believe the temp rose about 1 to 1.5 degrees in this time period.

If your film is consistently coming out over developed, you could shorten your dev time by say 5 to 10% to compensate. But it will come out in ball-park correctly developed.

In the past, I have maintained the temp by using pre-wet process and water bath then maintain the temp +/- 0.5C. It just isn't necessary in my own darkroom.

My current standard is to cool the developer to 0.5C lower than target to compensate for the initial rise. I typically use 20C (so I cool it to 19.5C) and either use specified time or decrease it by a little but when I do, it has more to do with contrast manipulation than anything else.