Few Questions

[The Amazing Spiderman]

Don't worry that much. By the end of that battle, you can then get better equipment for the mages, the robes, which increase the unit's mp more than a normal armor.
Ethers will be accesible as time passes and you finish missions. Just keep looking at the shop. But sometimes it's better to recover Mp in battle by a crystal....


Also, for the dorter battle, keep you wizard pretty well protected, and try to aim for the archers on the roofs with his magic. leave the knights to your other units. Since the Black Mage has low Hp and PA, you shouldn't use him for melee combat.
Maybe around Lv. 5 the battle shouldn't be a problem, anyway. Just level up a bit.

And finally, the only special way that your units will became extraordinaire units, you have to master various classes as the advance on the game. Just learn a lot of skills, so you can customize them to become powerful warriors.
If we go for stats, since you're beginning, just make your units stick with one type of units. If s/he is a fighter, make him/her master various fighter classes for a better stat growth. If s/he is a mage, master many spellcaster classes, for a better growth in MA and Mp.

Overall, leveling up your units as Monks, Ninjas and Knights will make your units decent fighters at the end of the game.

Leveling up your units when they are summoners o Wizards will gain them more Mp and MA, making pretty good at casting spells at the end of the game.

But, before all of it, enjoy the game, it pretty fun at the first time you play it, and by the second time, you might want to acomplish many things, like stat growth, get rare items, master all the jobs, understand game mechanics, etc, there are many things to exploit in this game, that I'm sure that you'll play it for a long, long time.