Some other random thoughts:

1) In the time you have between now and surgery (or chemo if you go that route), try to get all the relevant genetic tests possible done: at least a germline test like Invitae to determine any inherited mutations you may have.

2) It might not hurt to get a somatic blood test like Guardant 360 for genetic mutations of cancer cells floating around in your blood.

3) If you go with surgery first, ask your surgeon ASAP (because this stuff takes time to resolve) his/her process for saving tumor tissue and having some of it stored locally or sent out for NGS (Next-generation Sequencing).
a) NGS options include tests from companies like Tempus
b) "Live-state" tumor storage from companies like https://storemytumor.com/
c) Sensitivity testing from a company like https://www.travera.com/
d) ctDNA tests like Signatera for MRD (Microscopic Residual Disease); useful for ongoing assessment of treatment effectiveness or (supporting) indication of recurrence.

Travera had a free clinical trial going on last summer for testing pancreatic tissue. Since you may not know before surgery or before adjuvant chemo begins which drugs are most effective on your cancer, using the recovery time after surgery to get sensitivity tests done might help your docs start you on the best chemo first.

(e.g., even though Folfirinox is the regimen of choice for young, fit patients like you, it might not be the best. In my case, Gemcitabine + Abraxane + Cisplatin after the recurrence turned out to be way more effective. Had we switched to that part way through my neoadjuvant treatment, my outcome might have been very different.)

Regarding adjuvant therapy: If you go straight to surgery without any prior (neoadjuvant) chemo, after surgery you will still be a "chemo virgin" ("treatment naive" is the medical term, iirc). This might qualify you for certain clinical trials, including "vaccine" trials that you might not otherwise be eligible for. MSKCC always has a ton of trials going on, but every trial is time-consuming and tricky to get into. Ask about those options at your first opportunity.

Try to get at least one more CA19-9 test as a baseline before you begin treatment (surgery or chemo). Get the tests again after surgery as well, ideally at biweekly intervals. You might see inflated numbers shortly after surgery (due to inflammation, etc), but you should eventually see a downward trend, and eventually (ideally) numbers in the low/normal range. Don't stop there -- that should be your new, post-op baseline, which serves as the reference for successive tests to see if you ever start trending upward.