Hi Jon sorry to hear you've been diagnosed with this. You will find that a lot of people on this forum have been in exactly your situation, and I'm sure they will be letting you know their stories soon. My cancer was more advanced than yours so I had far fewer choices, and I'm glad about that, because it's a bit unfair expecting the patient to make a complicated decision when they are far from being an expert on the subject.
There is quite a strong psychological desire to just cut the cancer out and be rid of it. But the side effects of any treatment are not very pleasant, probably not as bad as other cancers, and in most people's opinion (but not everyone's) better than dying from the disease. If you have the stomach for it there is a lot to be said for surveillance, if you can tolerate the uncertainty of having the disease inside of you, which may (but may not get worse). Delaying the treatment for a few years will give you a better quality of life.
Some people would say it's only going to get worse so you may as well grasp the bull by the horns. I don't agree with that argument, I'd say it would be like having all your teeth pulled out and dentures fitted because you'll probably end up with false teeth at some time and you may as well get it over with.
So the above are arguments that surveillance is sensible, but the contrary is that the disease does advance and may spread, in which case not treating early will look very foolish. I think you have to keep a close eye on the doctors who are alledgedly monitoring you, there are stories of the disease's advance not being picked up in time.
I think most people on here would say with any G4 in the prostate it probably needs treating early.
In the end your going to have to make the decision about when to treat. Our stories are about our individual treatment they are not a scientific sample, but they may give you food for thought.