@mahnenrl
What I can to is give you my personal experience but I don't think I or anyone else can tell you what you can do or not do as we are all different.
1. Still able to work: I was retired when I got my 30 rounds of radiation but was avid exerciser. I exercised every day 1-2 hours.
2. Driving: Yes you can drive unless told not to. Are you taking a hormone? I drove 1 hour to my treatments and 1 hour back. Other than trying to schedule your trips to bathroom should be able to drive. For me I had to consume 16 oz. of water prior to treatments so waiting to do that until got there. Then made sure I used the bathroom prior to driving home. You mentioned fatigue I had it so minor but if yours affects you talk to your doctors.
3. Fatigue common: Yes but for me it was very minor. It did not stop my from exercising every day. But I could notice I was a little more tired when I did. Again I will asked if you are going on hormone treatments. I was not on hormones. It can have dramatic affects on some.

What was your Gleason score? Did you have tests like Decipher, PSMA? I mention those as I had them to help me and my doctors find the best treatment for me. Did your R/O discuss having the Space/Oar to help move colon away from prostate. How about drinking water prior to treatments to move bladder away from prostate.

I was 76 when I had my radiation treatments. Staying active, eating well, taking your vitamins and supplements (check with your R/O about taking any vitamins and supplements), and try to stay active.