as a step up from what the F22 carries in missile terms.
6x AMRAAM and 2x AIM9s is ~2500lbs. 6x 500lb missiles (like Sparrow) is 3000lbs. Meteor is 420lbs, in case the AIM260s are something like that. The "2x 1000lb, 2x AMRAAM, and 2x AIM9" load seems to be the physical max in terms of bay volume, and that's ~3200lbs.
Given the distances NGAD will have fly, it makes sense to carry more missiles than F15 or F22 natively do. Super Hornets and Eagle IIs have been showing ~10x AMRAAMs in heavy AA mode. So I went with 10x AMRAAM weights (~3500lbs) plus 2x AIM9 weights (~400lbs) for ~3900lbs, then rounded to nearest 1000lbs to get 4000. If the AIM260 ends up heavier, I would increase the expected weight carried to ~6000lbs (10x500, + 2x200)