If the difficultly increases after the coins are mined, then it would always be playing catch-up and actually a flood could occur.

It is my understanding (but I could be mistaken, there is a lot of FUD around BTC) that someone could in theory mine 500 hashes in a ten minute window then 'retire' having boosted the mining rate. This would not only net them a lot of bitcoins immediately but also restrict others supply of bitcoins.

Supply is roughly constant given a slowly increasing mining pool, supply isn't shock resistant.

I imagine they use a decent amount, but not nearly as much as would be required to run a cluster of computers to mine a comparable quantity. I think with an ASIC, electricity costs are negligible compared to the output.