There isn't a diminishing supply. Bitcoins are made so that they ever increase in supply.
No.
Supply diminishes short-term when block reward halves; increases short-term when network hashing capability is added (when power is added significantly, anyway). If you meant the TOTAL supply increases as time goes on, then yes, it asymptoticly approaches 21 million. But approaching an asymptote implies decreased acceleration. So any implied acceleration in your statement of "increase in supply" should be quickly quashed.