Vevictus, if you want info on side-quests, I suggest checking a walkthrough at gamefaqs.com. There’s just too much info to put in a post. (Quick hints though, you must have Mustadio in your party to get them and they don’t begin until at least Chapter 3.) Now just a couple notes for you here.

You can try a Samurai with Jump skill, but be aware of one thing: there is a damage bonus to Jump attacks if you are using a spear. So Samurai & other classes can use Jump, but don’t expect them to be as effective as Lancers unless you’re using Equip Spear. Of course, it can still do solid damage and will have the same great range, it just won’t be quite as devastating as a Lancer’s jumps.

Now this is purely a suggestion, but you may want to consider switching your mages’ secondary skills. (Or training them if you haven’t yet.) A Summoner with BlackMagic just seems a bit redundant, since both these skill sets primarily feature offensive elemental spells. BlackMagic might be a bit more useful for the Mediator. Unless you’ve got guns (not sure where in the game you’re at), Mediators are stuck with weak weapons & no offensive skills. But that’s just my opinion, you can configure your team in any way that works for you.

Good luck. Hope anything I said helps.