Any 3 of these red dots work fine w co-witness?
Yes, either for absolute or lower 1/3 depending on the mount you choose. Shooters choice on that. Absolute works very well with flip ups (no FSB) and leads to a more "natural" shooting position.
I'm assuming you have the M-LOK fore end system on your rifle as advertised by FN. Are you getting a BUIS set? It's not "need to have" but when you need it... reasonably priced set would be the Magpul MBUS polymer series. Works well for the "oh ****" situations.
As for lights and lasers. Are you talking visible lasers? If so, save your money for something else... like a sling and mags. Lasers are a neat doodad, little more. If we're talking for an NVG setup, that's a different story.
Sling, sling, sling. Padded works well.
Larue does an exceptional sling, but it's on backorder at the moment. And you'll need an M-LOK capable QD mount for that for the fore end. I'd suggest Impact Weapons Components or Midwest Industries. Check the Midwest Industries website, Brownells, Primary Arms or Palmetto State Armory.
Mags, mags, mags. I tend to stick to what I know and have used. I stick to Magpul M2 or M3, Lancer L5AWM opaque, E-Lander (gotten quite expensive these days, but they are bulletproof) or standard aluminum mags of the D&H, Brownells or Okay/NHMTG variety. Ten to start.
We can talk triggers, charging handles and muzzle devices if you want in another post. Oh, and drop an H2 buffer and Springco Blue in that thing. You'll thank me later.
As for lights, the best money can get is (IMO) the Surefire Scout Pro. 1,000 lumens in a compact package. Check around for the best deal.
Avoid the following dealers:
Botach Tactical
Cheaper Than Dirt