Team for Navarre?

Well, it mostly depends on how you build Navarre. You could go with a simple build for him.

Slaying Edge+ (+Spd)
Reposition
(Special Skill)
Fury 3
Desperation 3
Flexible C slot
Speed +3

Another unit for a team could include someone who can deal, and take, magical hits. I recommend Saias since not only is he a blue unit, but he's also a Ploy boy, although he can't run Fury as good as Arvis, but if you don't mind having 2 red units on your team, then Arvis can be good. There's also Micaiah, Julius, F!Morgan, Deirdre, and more.

A unit for the 3rd slot can be someone that can take some physical hits. Preferably someone that's not red. Lukas, Beruka, Subaki, and Oboro are a few options. There's also armored units if you don't care about their lack of mobility, like Gwendolyn and Sheena.

For the 4th slot, you can pick someone that's a support unit. Olivia, or any singer/dancer for that matter, can be a huge help for your team, especially for Navarre. You can also pick Corrin or Eirika (if you didn't pick Julius, or another red unit. Don't want 3 red units on one team, lol) for support. There's also the possibility of a dagger unit. Sothe is good since not only does he debuff the enemies, but he also buffs his allies in the same move (if they're close enough).