If you aren't RNG abusing, Sedgar and Wolf are both very useful options, as they can pretty much guarantee a good amount of Def. For people who care, here's my personal chart of Def magic numbers that I keep in a notepad document for reference.
Hp and Def
----------
* Hp+(Defx2)>98 allows you to survive one round of anything. This is the
number most characters shoot for. It is most easily obtained by 59Hp and 20
Def, or something around there.
* Hp+(Defx4)>168 allows you to survive two rounds of a Swordmaster while
wielding an Axe. Subtract 4 from 168 for if you want to live while wielding a
Sword, and subtract 8 if you want to live while wielding a lance.
* Hp+(Defx3)>140 allows you to survive a Longbow shot and anything physical
following it.
* Hp+(Defx3)>124 allows you to survive a Longbow shot and a Swordmaster attack
following it.
* Hp+Def>87 allows your mounted units to survive one round of a Berserker Pole
Axe
* Hp:Def>81 allows your mounted units to survive the most powerful Ridersbane
attack (That is, one coming from a General, the lance-wielding unit with the
highest Str cap).
Format miight be messed up from the copypaste from notepad.
EDIT: Forgot to add the actual point of my post. If you're going to be playing on normal mode and arena abusing for you're run through, I'd recommend Radd instead of Navaerre, as he gernerally turns out better. Also, forged Brave weapons are much more powerful than the Hauteclere, Parthia, and Mercurius. Also, if you use reclassing, Sedgar and Wolf should really have much, much higher stats than most of your units (Assuming you didn't get really lucky or RNG abused); however, you seem to be too far into you're playthrough to do this again. Anyways, Xane can be handy, as some people end up devoting too much time to a certain character and are not able to get another one to a decent level. The whole imitating thing is generally too much of a tactically disadvantage to be bothered with, so try to avoid it. Hope I helped!
Note: My Wi-Fi guide for FE:SD will either get accept or rejected by GameFAQs within the next few days. If it get uploaded, I'll post a link here.