If you bless them in church after every fight it only takes 30 seconds. It's a bit annoying but that way it doesn't take up much time.

The reputation, xp and silver reward is constant per AP spent so yes, doing lower maps doesn't cost you anything in that regard. It's still preferably to do the harder maps as the drop rate for them is higher and you get a (low) chance of having the Ioros robe drop.

The robe is a pretty good armour with hp, defense and movement speed on it