Question on a Barb/Fig feat and armor

Hi all! Sorry in advance, this might be a bit of text. Thanks for reading!

I beat the game as a goody two shoes Gloomstalker Assasin durge and had lots of fun. Saw most of the content available to good characters and just all in all a good time.

Now, I'm feeling like going the other way around. Half-Orc, Berserker/Fighter, embrace Durge, murderhobo playthrough. Melee crit build.

The idea would be to wear full Bonespike set with the Hellfire Greataxe and the Amulet of Greater Health, and crit fishing - so the stats would be:

17 STR (becomes 22 with Hag Hair + Vigour Potion + Mirror of Loss) -> Can be 24 with an ASI, question on that later

16 DEX (14 before obtaining the amulet)

8 CON (23 with amulet, 16 before obtaining it)

8 INT

14 WIS (10 before getting the amulet, mostly for saves)

10 CHA (8 before amulet, just because of spare points and avoid negating a point in Intimidation checks)

The split would be 9 Berserker/3 Champion. With Dead Shot, an Elixir of Viciousness, and advantage (thanks to reckless attack) that would be a 40% crit chance, synergyzing with GWM. I'll only get two feats and one will definitely be GWM, so the first question is: is it better to take an ASI for 24 STR, or stick with 22 and take Savage Attacker?

I also know that the Helm of Sarevok can get me to 50% crit chance, which is amazing - but it counts as medium armor, which conflicts with Unarmoured Defence. The second question is: Would Sarevok's helmet be worth it in this case? If it is, what good medium/light armours would be best to pair it with?

Finally, the main idea is to murder everything except companions (though I know I'll lose Wyll and Karlach), but I know that plenty of useful items are locked behind some small sidequests (like the Ring of Protection in Act 1). I don't mind playing along, getting some of these rewards, and then killing everyone. So the third, and final question, is: What items earned via sidequests contained inside a single Act would you recommend obtaining before killing everyone?

Thanks in advance!