Help With DIY Emerald Legion: the Immortal Do-Nothing

[Anthrowhale]

We have fire resistance, but a fire shield would be nice. A fiery tunic and/or a crown of flames could help there.

Searing Spell does not care about fire resistance. It cares about fire immunity (which causes damage to be halved) and it cares about fire shield (since it is still fire).

Are Fey spirits? Regardless, would the Unseeley Fey Summer's Caress not provide the same benefit as Fist 1?

Yes, and yes.

I'm slightly unclear on what the goal is here. For example, are body-swapping tactics allowed? Initiate of Mystra? Planar traits?

For example, a Dragonborn Telthor Initiate of Mystra using Selective Spell[you] Antimagic Field is immune to all magic-source damage and all mundane source damage leaving only a handful of damage sources which count as magical while working in an AMF (Serrenwood, Soulknife, Orb of Force). It's available at ECL 11 in persistomancer form with level buyoff. Maybe add in Starmantle and Evasion (via Spelldancer) while keeping Forceward handy to finish off vulnerabilities.