I'm not going to implement the skills system... Probably. It has the potential to be either incredibly limiting for the player or create some impossibly strong characters if the RNG favors them.

This world exists because the world that the deities used to exist in has developed to such a point where they're seen as irrelevant and unneeded, and thus created the new world to... Well, to put it bluntly, to be looked up to/worshiped again.

Similar to DanMachi, currency can be obtained from monsters and their drops by means of trading, so it's perfectly viable to be an adventurer. 

The motivation for the character... Well, that'd probably be up to the creator. It's a world based around exploration, so people could be motivated by money (as mentioned before), fame, or the thrill of finding something new... Just to name a few examples.

The gods seal their power away for much of the same reason as in DanMachi- so that none of them have too overpowering of an advantage over every other. It's kind of a measure to make sure that nobody gets shafted and everybody technically has a chance in the spotlight (as was the case in many myths, as we've seen). It's also fun to champion an adventurer who does something huge and get part of the credit for it... Or something like that.