TIme to hold a line at the junior bases is less than the time to finish OE. So unless you're intending to bid reserve to leverage seniority into specific days off, I wouldn't factor reserve rules too heavily. Global Reserve notwithstanding, of course; if you bid 777/787 expect reserve for years. But at Delta you wouldn't be int'l widebody for a while anyway, so maybe that's a push.

As for seniority, I saw a slide somewhere that said 50% of the United pilot group will have turned over by 2030. To put it another way, as a new hire you'll be 50% seniority in 8 years, assume no growth or shrinkage. If true that's an amazing thing to think about. I have no idea what long-term seniority looks like at Delta though, maybe it's even better. Either way, yours is a good problem to have. Good luck!