When it comes to the basic must have calibers, you are on the right track. Some decent suggestions have already been mentioned. I’ll just throw it in my .02
9mm, 5.56, .308, and 12 gauge are the most available ammos on the market and in the widest use.
Lots of affordable, good quality ARs are available. The S/W M&P 15 is definitely an affordable and dependable option. PSA has good inexpensive options as well and uses quality parts like the toolcraft BCG. Bravo Company, Colt, and Sig are also great options.
I would never own a 12 gauge that was magazine fed and trust my life to it. By nature, they are finicky and do not run low brass shells dependably ever. The mag fed versions are just for toys. Value to quality in semi auto shotguns, my nod goes to Mossberg 930. If you want the best then Benelli M2 or M4 or the Berreta 1301. Forget the magazine and just learn how to reload while walking.
Longer range 308, bolt action is the most cost effective option and the veritable Remington 700 is a great choice. Another option for me would be a Ruger precision rifle. If semi auto is preferred PSA or Aero in an AR10 style would be entry level good quality. Top tier would be LMT or KAC.
Pistols are personal, Glock gen5, S&W, or Sig are all dependable so buy what fits your hand and shooting style the best. You could buy a 1k AR, the 930, an (PSA) AR10, and a pistol for under $3500. You could purchase decent optics for all the rifles, and still be under 5K