I would neither max Con nor pick up Tough. 14/16 is plenty for a Barb unless they're planning to go naked, and even then, Amulet of Health exists.

I also agree with Dr. Samurai. Almost all of my Barbarians are grapplers, so maxing Str goes beyond adding a couple of points of DPR, it also means you're less likely to waste your action. Moreover, having Max Str can contribute to your DM deciding you don't need to roll at all for various challenges.

I agree with the overall point that feats are very important for Barbarians, but I primarily view that as a reason to multiclass Fighter and get more of them.