Both of my builds, the Fighter/Paladin and Fighter/Barbarian, have a crazy high AC. The Paladin version would have plate, shield, and defensive fighting style for a 21 AC without magic. The Barbarian version has an unarmored AC of 22.
The frenzy Barbarian still has melee resistance while raging, but I would probably go Bear Totem if it were my build though. The exhaustion levels from the frenzy barb is just too harsh in my opinion. You can gain those extra attacks through feats anyway. The Battle Master Fighter is strong, but I like Champion better for a build like this. I think it fits the Barb theme best. You get the awesome extra crit chances, two fighting styles, the extra athleticism, and the 12hp regen you'd get per round when injured. The Barbarian class is made for crit fishing and so does the Half Orc race.
Three levels of Rogue(Assassin) is only going to give you 2d6 sneak damage and yes, it's set up to have a monstrous first round.
So unarmored AC would be 22 because of 10+5dex+7con?
How would you get extra attacks from feats, i don't think i saw any like that?
Also how would you go about leveling this level 20 bear totem barbarian/20 champion fighter? Start as fighter go to level 3 then barbarian to level 3 and then both to 5? Which one should be taken to 20 first or do i level them kinda equally?