How does offer creation impact fund requirement of an account? How much does each offer created increase the XRP requirement on that account?

Does it relate to PayerGets?

Is it cleared once I cancel the offer?
Every entry in the state tree of the ledger requires 12.5 XRP reserve, it doesn't matter if it's a trade offer or a trust-line. When the entry disappears from the ledger (by getting filled or being canceled), the reserves can be moved again.

The only exception is the account entry, which requires 50 XRP instead of 12.5 XRP and is perpetual (because accounts cannot be deleted).

See https://ripple.com/wiki/Reserves for details and the current reserve requirements (they can and have changed).

It is not related with the field TakerGets of the message OfferCreate.