Dedue as a Wyvern Rider is definitely not possible at this point, I've been training him to become a war master. I feared that with his absence in some chapters after timeskip it would be hard for him to catch up, so I didn't funnel much exp into him and focused on Byleth, Dimitri, Felix, and Sylvain instead.
Hilda's already on my team, so I can replace Dedue with her as my semi tank I guess. I was also thinking of Leonie to replace Ashe (though I guess Ashe could still function as a deadeye/waning shot user for support???) as my secondary bow knight, with Felix being the primary one. I was actually considering making Ingrid my dancer too. She has decent spells, decent avoid, and it's not like she'll be contributing much as a flier anyways when her strength has been abysmal for me.
How many physical combat units should I generally focus on? I already have four in Byleth/Dimitri/Felix/Sylvain, with Hilda and possibly Leonie being the 5th and 6th one. My regular team comp would look something like this:
Byleth - War Master
Dimitri - Paladin/Great Lord
Felix - Bow Knight
Sylvain - Wyvern Lord
Hilda - Wyvern Lord
Leonie - Bow Knight
Catherine/Petra - Falcon Knight
Mercedes - Bishop
Annette - Dark Knight
Ingrid - Dancer
Utility characters:
Marianne - Gremory/Mortal Savant (?)
Dorothea - Gremory
Linhardt - Bishop