You don't need a full party at all. We do it with three, a warrior, white Mage and scholar. The only fight with any challenge is the chimera one.
Ideally, you want DPS, healer and tank. Less people to split the treasure.
Treasure isn't split, you either receive 1,692 or 5,076 Gil. It's much more beneficial to the whole group if you have a full party, each with at least 1 map