Wow this thread is really active
Someone asked about battle mages; battle mages are absolutely terrible until at VERY least level 20 but 25 or so is better. The normal combo is not very good until you start getting some buffs. I'm personally maxing colorless because I am a big fan of move speed, and you can get your first one from autochaser anyway.
On Crusaders all I can offer is theory fighter but the sp on battle crusader is loose enough that you can get the good aggressive buffs (jew star) and still max the better attack skills. They really have a hard time being as effective as other aggressive classes though afaik because all their skills are fixed damage instead of based on matk, so they don't go up as much based on your characters level etc, you have to level the skill for it to be effective. Support crusaders are really easy to build, just max the better support skills, and you'll even have room to get some of the more supportive attack skills (like spear and wall which have utility outside of just damage). Levelling them just depends on how social you are hahaha
I guess I'm in no position to second the advice about concentrating on one or two characters but it's a good idea. You just need to find people that play the same time you play and party with them so you can level through the tough spots. The game is completely different and a million times better with a party.