Sights - Some fiber optics with windage adjustment will help you align POA and POI (point of aim and point of impact) and help keep your head down on the stock better than the plain old front bead. Scopes can get you there even better, but also more expensive. My gun luckily shoots every load where I aim it with cheap stick on the rib truglo gobble dots.
Chokes - Tons of great choices here.....simply do a search on "870 Choke" and you will see alot on here like the Kicks, Jellyhead, Indian Creek, and Sumtoy will make anything you want them to.