Consider that your units from the left and right side are set up as:

^^^^^Front Facing^^^^^^
Unit 1L Unit 2L Unit 3L
Unit 4R Unit 5R Unit 6R

The second unit in the front left side will take the brunt of your damage when dealing with frontal attacks. Therefore, your tankiest unit needs to sit in the second slot. You can have other front range troops sit in the 1st and 3rd slot, but know that when you are taking damage from an angle, that is when they will take more damage.

This also works for your back row, but you want to take a different strategy. Your 5R unit should be the weakest unit. 4R and 6R may get some fractional damage when confronting enemy from a suboptimal position. If they can at least soak up some damage without instant death, you should be ok.

Since the first beautiful, black, bumpy wizardry I box was released over fourty years ago, the subclasses have been always a challenge to try to create. Those would be your Lord, Bishop, Ninja, and Samurai. You could only create those classes if you had a minimum number of stat points across the spectrum to promote them from one of the base classes. With Wizrogue, you will likely draw these premium units with your regular draws. If you examine a base class versus a premium class within the same ranks (e.g. common, uncommon, rare, etc), you will notice that the premium classes have HUGE stat advantages. I would recommend that you should focus on those characters versus the base classes simply because they have 10+ points more in primary stats.

While you can get pickier later looking for classes that have better race/premium class combos, you can't go wrong starting this way.

One last tip as you added these members in: don't feel shy using your experience items to raise any of them up fast. Sun, moon, and star pieces have special values to change ranks from common, to uncomon and so on, but anything else should be considered fair game. You will get stuck in areas if you don't aggressively purchase and use these items.