16" AR15 with an mlock foregrip that's at least 10" long, a good rifle light, sling, and at least 7 top teir non-plastic 30 round magazines. (I prefer the aluminum Duramag for defense use.) Start with good metal sights and try a bunch of sighting systems (I prefer 1x prisms due to an annoying astigmatism).

You can start with a PSA build or spend a bit more and get something better, but do not go crazy with your first AR. (Usually. Unless you want to buy a basic BCM, SOLGW, DD (not a preferred brand for reasons of them supporting the steppers way too much, but they make really good rifles).)

1000 rounds minimum of M193 or M855 depending on what shots better groups through that rifle. Plus training ammo. (Same concept as spend and replace.)