You cannot AoA on the same initial round that you Rage, or your rage will end immediately (since you haven't taken damage or attacked anyone since your last turn). AoA needs to be pre-cast in the hour before battle, or cast after you take damage (so Rage doesn't end). But once you do that, then every enemy that strikes you will take 25 damage per strike until your AoA HP run out.
20% lower HP from the Warlock class can be offset either via Fiendlock or AoA temp HP or by casting Vampiric Touch to heal. There's not that much difference really between having 89 HP as a Con 16 Barb 2/Warlock 8 vs. 105 HP as a Con 16 Barb 10, especially after you factor in various sources of temp HP and healaing. All it takes is one Lore Bard on your team who heals 70 HP with a 3rd level slot (or a superhealer who heals 240 HP with that same 3rd level slot) and that 16-HP differential shrinks to insigificance.
There's lots of options. At the moment, Barbarian 2/Death Monk X feels like the most interesting "pure warrior" option to me. An ultra-mobile Barbarian who occasionally power attacks you with his greataxe (40ish points of damage) and punches you in the face twice (Flurry of Blows + Stunning Strike) sounds... amusing. It would be somewhat MAD because of the Wisdom dependency, but even with relatively medium stats like 5 15 13 12 10 14 you could consider it, and [two rolls later] 15 15 9 14 5 17 could be hilarious. Str 18 Dex 14 Con 16 Int 5 Wis 15 Cha 9. Normally I dislike playing low-Int characters (not enough tactical flexibility) but with a Death Monk/Barbarian it genuinely is appropriate--when you see something hostile, run up and smash it until it stops moving. Feats: (1) Great Weapon Master, (6) +2 Str, (10) Resilient (Wis).
While wielding your greataxe and wearing armor, you miss out on the increased Monk unarmed damage and the extra movement, but you can still do Flurry of Blows, at advantage for Reckless Attack. Once you hit Death Monk 11 your ki will be reserved almost exclusively for Flurry of Blows + Mastery of Death. When you feel like being an intimidating, scary tattooed barbarian instead of a face-smashing hulk barbarian, you can spend your action to frighten everybody instead of smashing.
If I were in a certain kind of mindless mood this guy could be a lot of fun, in the right group.
That is pretty neat, another thought I had about the warlock. One needs to keep in mind that multiple sources of Temp HP's do not stack. So, I would keep that in mind if you were thinking of multiclassing both battlerager and warlock. You only get to keep the highest... and with a lowish Cha, I think you will find the battlerager will likely give you more per round.