From what I see you should be pushing on to Fiery Oasis to farm it is better than Dragon hunting/Return to Ruins for unit XP.
As for your army you have most of what you want for your core army. I would assume you will level the second heavy, the 3rd single target healer (like you said), and Imelia as a 3rd duelist (even as a -2 CR 5/10 skill) should be a good addition. From there, unless you have a strong desire to expand before leveling more, I would push toward 50cc30/40/50?, and then (or at the same time) focus on you first few AW's. Probably something like Spica > Iris-Katie > Bernice. Unless you have a Gold Get, Drop rate increasing, or team wide stat boosting unit.
With that said I'm not as knowledgeable, nor as experienced, as some of these other guys. So, if they say something different they are likely correct. Good luck!