Millions of people visit Greece every year and I’m willing to bet that a lot of them don’t speak Greek. It is a very popular holiday destination for English speakers. I can't imagine that you would have a lot of trouble at all1.
Immigration and customs should not be a problem. Make a note of your hotel name in the unlikely event that you have a taxi driver who does not understand where you want to go.
1. Source: My wife visited Greece a month ago many years ago without knowing a single word of Greek beforehand.