Welcome aboard Andy,
So your journey seems to mirror mine in a lot of ways. I started with PSA score of 4 back in June. My MRI results were similar toy your but only PI-RADS 5 and all in left section of prostate. I had the same biopsy as you have lined up and to be honest it was plain sailing (a bit embarrassing but easy enough).
The biopsy will confirm the cancer diagnosis in the prostate if that is the case. To the best of my knowledge the MRI does not confirm the diagnosis but just that there is something there thats needs further investigation.
If you go down the same path as I have been it will be a CT scan if the biopsy confirms cancer. This will show if it has spread. If this comes back clear then you may well have a PSMA-PET scan that will confirm any small amount of spread.
I'm currently waiting to see the surgeon to discuss if surgery or RT/HT is the best treatment plan for me.
As far as I'm concerned, the medical teams are still looking at this as a curative path and not just managing the disease.