Now that the training missions have opened up, you have access to Zanele, Khamari and - in my personal opinion - the best unit in the game, Benji.
You want to go ahead and immediately reclass Zanele into Tamer and pick up the perk for her personal skill to gain more gold.
Khamari is content in his base class. He will be one of the handful of units that can tank a hit or two in demonic. He will eventually fall off later, but he does make a reappearance in strength with level 25.
If you want the best unit in the game, reclass Benji into a Nightblade - he can use a generic dagger for now. You want to pick up the self cast for the speed as well as either the mana or the debuff cleanse for his personal - eventually, you'll get both.
I strongly recommend keeping your units leveled to within 1-2 levels of your highest level character through the training missions in demonic because the training missions are actually a challenge keeping every unit alive - let alone an under-leveled one.
Additionally now that you have access to training missions and both Khamari and Zanele, I would focus on bond levels. This will give you access to a lot of ring options as well as gold to buy things in the shop - like that Elixir of Might you might not have had enough gold for last chapter. The easiest way to knock out a majority of it is to have Riordan fight enemies next to all of his bonds and have Khamari fight next to Benji and Zanele. This is like 1/3-1/2 of all your bonds so far. Then just focus on specific gems you need.