All of what you suggest could happen. Your PSA could stay stable or it could rise. Going to the same lab each time will give you more accurate results, It can vary if you go a different Labs.

I know people with a Gleason nine that have come to ancan.org Advanced prostate cancer meetings talking about how after 20 or 30 years following a prostatectomy their PSA started rising. There is one today at 6 PM Eastern time.

If your PSA does hit .2 you should meet with an oncologist about getting salvage radiation. The following article discusses when you should do that.

From Ascopubs about what PSA to do salvage radiation.
≤0.2 ng/mL:
Starting at this level maximizes disease control and long-term survival. Patients treated at PSA < 0.2 ng/mL achieve higher rates of undetectable post-SRT PSA (56-70%) and improved 5-year progression-free survival (62.7-75%).
Delaying SRT beyond PSA ≥0.25 ng/mL increases mortality risk by ~50%.

0.2–0.5 ng/mL:
Still effective, particularly for patients with low-risk features (e.g., Gleason ≤7, slow PSA doubling time). The Journal of Clinical Oncology recommends SRT before PSA exceeds 0.25 ng/mL to preserve curative potential.

0.5–1.0 ng/mL:
Salvage radiation remains beneficial but may require combining with androgen deprivation therapy (ADT) for higher-risk cases.

This article discusses the above;
https://ascopost.com/news/march-2023/psa-level-at-time-of-salvage-radiation-therapy-after-radical-prostatectomy-and-risk-of-all-cause-mortality/
Your Gleason score is a major factor in reoccurrence. If it was a seven year, PSA may never rise high again. If it is an eight or higher than reoccurrence is more frequent.

You got prostate cancer quite young. That is frequently because there is a genetic issue.

Getting an hereditary, genetic test is a good idea. If you have certain genetic issues, there are new drugs to treat them. You can get one free here

Prostatecancerpromise.org

They will send you a kit and in about three weeks a genetic counselor will call you to discuss the results. Don’t check the box to have your doctor involved. In that case they won’t send anything until they speak to your doctor.