The first Gulf War began in 1990, and the Iranian Revolution took place in 1979. The causality may well have taken place in the reverse of what you suggest.
Yep. You'd think if the reason the US restarted their war with Iraq was using Euros as a reserve currency, they might have made a bit more fuss about those pesky Europeans creating the Euro with the explicit goal of being a global reserve currency a few years earlier...
Being the largest reserve currency has more costs to the US than benefits overall and policy has been to try and reduce that exposure for the last decade or so.