Wow, you are a great strategist! Instead, though, I usually grind on arenas for Guy and Raven to promote, keeping my troubadour at a steady 15-20, since when she gets the chance to attack she isn't great. So when I max her out at 20, I use my guilding ring on Canas, Lucius, and Erk instead of her and Serra.
Once done with that (I tend to steer clear of Knights and slow, yet heavy units, I bench Oswin and Wallace for the entire game), I usually try to Level my Lords and the axemen (Dorcas, Bartre, and Dart) to promotion level as well. Unfortuantely, the damn game killed off Dorcas and Bartre when I had them both at Level 19 (Arena claimed Dorcas, I didn't bail quick enough) and Bartre was killed in a fog of war map by archers that I couldn't see.
I lost my airborne units through me using them on the desert level trying to unlock Genisis and gaining the items (got the items but not the sidequest). And I lost my cavalry because he got gang banged on the pirate level.