If UA mainline jets work for you, then definitely go with Economy Plus. Since you don't have UA status, I'd probably pay for it for a year, then keep status so you don't have to pay to renew E+ the second year.

Asking for exit rows work on Delta once you have status, but you also have to buy your tickets well in advance before the seats fill up, and/or watch the seating charts several times a day 5 days, 4 days, 3 days, 2 days, and 1 day before flight date.