Each Choice, Explained

[Rejuvenation] will provide myself and nearby allies, my shadows included, with a little bit of healing over time. It doesn't counteract their decaying health but it can mitigate some of it.

[Power Drift] and [Blind Rage] get me to 214% Ability Strength exactly with one mod slot and the Exilus slot. At that threshold, Shield of Shadows reaches a maximum of 89.88% damage reduction; the cap on the reduction is 90%, making those two the most space-efficient combination to [Reach] the number.

[Despoil] keeps my health below maximum so I can take advantage of [Equilibrium] to mitigate [Blind Rage]'s penalty, [Health Conversion] to further mitigate incoming damage, and Arcane Pulse to keep myself and my team topped up.

[Vitality], [Stretch], and [Primed Continuity] are the most numerically powerful mods that provide their bonuses; more Health means I get more out of my mitigation, Ability Range means my shadows and I can range further from each other without endangering [Shield Of Shadows]' mitigation, and in spite of Overframe's UI saying otherwise Ability Duration over 100% will reduce Shadows of the Dead's health decay rather than increase it.

Arcane [Guardian] is just more mitigation to keep me alive longer.

Lastly, subsuming Blood Altar brings a little more utility to your team beyond Desecrate alone and using it rather than recasting Shadows of the Dead just to heal shadows is both more energy efficient and more helpful to the team at large.

When selecting a Companion, the Synth set's mods for them key into my Health Orb synergies. I prefer either [Smeeta Kavat] or [Panzer Vulpaphyla] for gathering loot or excellent sustain, respectively. If taking Smeeta it's worth mentioning that its [Charm] is more likely to proc its double pickup ability if only a melee weapon is equipped since not carrying a reloadable weapon will take the Instant Reload ability out of the pool of potential abilities.