I am slightly biased on this question
I am English, live in Spain and work for a US company.
Good English is important - but focus on comprehension. A lot of overseas reps have great written English - but often they cant understand the point that is being made.
Anybody you take on as rep will be experienced in the industry so they will be used to working strange hours to fit in with US timezones.
I will take the fifth on the subject of salary.