Just spit balling, not an expert...

I like your dr's plan. If the MRI is negative, great. It's not end all be all of diagnosing this, but, if there are no lesions and the PSA doesn't rise too quickly...AND you're okay with surveillance... I'd say that's due diligence.
If there's anything suspicious you'd probably want the biopsy at that point.

If you're concerned but don't want to do invasive tests like the biopsy without more info, maybe a second opinion would be a good idea.

regarding the PSMA PET / CT given the cost of same, the insurance folks would probably not approve the PSMA unless there was a finding on the MRI followed by a biopsy. (that was my case anyway)

Also, in the article quoted it states the FDA approved that scan "....to identify suspected metastasis or recurrence of prostate cancer"

Of course things may have changed since that was written.
Best of Luck to you!