How many times can I contact a potential employer?

I interviewed with a company almost a month ago for a marketing position. Two weeks later I was called back in for a second interview with the head of the department. He told me there was a position open for department coordinator, on top of the marketing position.. I expressed my interest for both of the jobs because I really want to work at this company. I followed up with an email within 48 hours of the second interview. He responded 5 days later with this: "If the position is available, would you be interested in the department coordinator position? when is your available start date?" I replied promptly and now it's been 8 days and I haven't heard anything back. I'd love to email him back again but I don't know how to word the email or if it's even appropriate to contact him again since I've already written a follow-up email. I don't want to pester him, but I really want this job. Any advice?