Yeah I've been planning out my permadeath teams as well, I don't want to stack one too heavily so I'm spreading it out a bit. I want to make sure I have one absolute bomber on my 3 teams, so I spread out Nino, Linde, and Reinhardt.
A: Nino, Robin, Jaffar, Olivia (I kind of want to go Lachesis here instead of Jaffar for healing if they do spawning enemies)
B: Roy+1, Azura, Linde, Fae (Again might go Maria here instead of Fae depending on the mechanics)
C: Reinhardt, Eirika, Nowi, Kagero (maybe 4* Michalis+1)
D: Hinoka+2, 3* Olivia, and left over 5*s (healer + fae, or healer + jaffar)
Then around 20+ bunch of 4* level 40 character to spare including a pony emblem team. An arena match with our A teams would be fun to watch play out.
Edit: Also just pulled a 4* Klein, do I keep him or put Death Blow 3 on Nino?