Sorry you find yourself here.
There are two significantly different treatment paths, and that depends if they think the cancer is curable, or if it will have to be managed lifelong. Until you have the results of the bone scan back, you won't know which path, although it does sound like there's a significant chance it's going to be something that needs managing lifelong. Incidentally, although I used the word curable, it's generally regarded that PCa is not curable (in common with most other cancers), but curable means you end up in remission until you die naturally of something unrelated.
The conventional treatment path for curable T3a PCa would be Hormone Therapy (HT) and RT. The conventional path for lifelong management would be HT and chemo, usually later on.
You are right in that research has shown chemo can work better on both paths when used earlier - basically, throwing everything at it at once. This isn't universally done though - it's quite new, and depends heavily on the health of the patient, quality of life considerations, etc. I suspect the nurse is broadly referring to chemo for lifelong management, versus radical RT for treatment with curative intent. Radical RT would not be used unless it is thought to be curative, as it would give all the side effects and no benefits - it's to prevent spread before it starts. The finer details of the treatment will be decided by an oncologist, not the nurse though.
Wishing you and your dad all the best.
Meanwhile, you might want to prepare for the appointment by writing a list of questions, and being reading to write down what the consultant tells you. You may well get more than one treatment option to chose between, which you need to go away and think about, and of course ask for opinions here if we can help.