MCP: Get Rates, Purchase, and Refund Questions

Can a token retrieved through MCPGetRate be used for multiple purchase transactions across different customers while it is still valid?  For example, if customer A requests a rate token for CAD/NZD, and customer B requests a rate token for CAD / NZD a moment later, can they both use the same token?

Does the Card Holder amount need to match the purchase amount? 

Are there different rate tiers such that the exchange rate for CAD/NZD is different between 1 $ CA, 100 $ CA, 1000 $ CA?

Can a rate token retrieved using a the 'P' input parameter be used for Refunds (the 'R' input)?  Do these two transaction types need to use separate tokens?