For 1st classes, why not just keep the official quests and possibly add character-bound, low weight and class-specific gears with not-overpowered, yet useful, effects (kind of what some servers do with
BG gears or "
rental items")? It could be something like
these, for example.
To make sure that new players will know about it, you can easily add a few messages to the
Welcome Lady NPC. She could also give a little information about custom content to them, either automatically or via a new option in the menu (or just recommend everyone to check the wiki and forums regularly, which is easier and faster lol).
For 2nd classes, add small rewards for chars at job 40~44, a little better at 45~49 and something good only at job 50, to encourage people to work harder and make it be worth the effort.