I suggest using:
3 Azure Archon Shards with +Energy Max.
2 Emerald Archon Shards to fully strip armor with 4.

OVERVIEW/MATHS:

Okay, so let's look at some math (boring ik). This is using this site: https://hypothermia.cc/tools
Let's start by looking purely at base STATS and the current MODS.
9.333 hp and 936 armor results in 29.341 EHP (10x with [Adaptation] (This will apply from now on, even if I don't mention it))

If using [Jugulus Carapace] instead of [Primed Vigor] you would have 28.439 EHP. (10x with [Adaptation]) (Oh how the tables have turned :(....) However if using Jugulus you can save an umbral forma and still have exilus

You can use Eclipse for a damage boost or you can use it for 75% damage reduction which gives [Inaros] 1.173.660 EHP

DAMAGE:

Yes no [Inaros] can do some nice damage. You can use 2 to group up enemies (I use Vazarin Void Snare on top) AND open them up to FINISHERS. Thanks to the new Melee Crescendo, you can then build PERMANENT 12x Combo multiplier :O
So you go in a mission. Press 2 and group some enemies. Finisher kill them (look down at them and press E). Build your melee combo. And boom, now you have a melee that does MILLIONS :O of bleed damage on heavy attacks. Talking about the [Reaper Prime]! Reapers have forced bleed proc on heavy attacks, so this weapon is our perfect candidate, here is the build!
MILLIONS OF DAMAGE PER HIT

You can also use 4 to 100% armor strip enemies if needed.

Now we have a pretty tanky and braindead frame + a weapon that will one-shot most enemies probably up to a couple thousand levels. Finally, Inaros can do something (Except if the enemies deal so much damage by then that he gets one-shot too lmfao)

ARCANES:

Arcane Grace will heal you up all the time
Arcane Avenger for crit bonus since you always take health damage

No matter what. You might think he is the tankiest because of his health, but in endgame, you mostly rely on CC or shield gating to survive, the enemies deal more and more damage the higher the level they are, for example:
-Inaros vs lvl 1 to 199 enemies : joke
-Inaros vs lvl 200 enemies : fair fight, you might need lifesteal to survive
-[Inaros] vs lvl 201+ enemies : [Inaros] 1 shot
(^Investing in defences only push further the lvl cap at which you'll get 1 shot.)

I think the only reason to play him is if you are playing "low level" missions (1-200) and just want to play a chill playstyle. Enjoy!

COMPANION:

Panzer Vulphaphyla for priming. Vulphaphyla Build)
^Just use [Link Vitality] instead of [Panzer Devolution]

FOCUS SCHOOL:

Vazarin for another grouping tool (It groups them even tighter and you can heal yourself in case you get low even with Arcane Grace)

Build Showcase
(^Outdated Video)