Hi Lou, don't forget to ask the basic questions:
1. What options do you have,
2. What is thought to be the best for your case,
3. When will it start and how long will it take.
4. Where will it take place.
As Tony says the Oncologist might steer you towards Radiotherapy so you might ask why it's better than surgery in your case if they do.
On the other hand I wouldn't let the decision drift and take a lot of time thinking about it. With Radiotherapy there is likely to be almost immediate start of hormones whereas with surgery you will be waiting for an operation appointment although that shouldn't be a reason not to take surgery.
I'm not sure how you got to see the oncologist as I was asked by a Urologist which treatment I wanted and then went to see only a surgeon.