re: How long before you send the follow up email

I would say that it's generally good practice to send a follow-up email within 24 hours, with just a couple of short lines thanking them for their time.

But since you were doing more than a perfunctory entry-level interview, I'd say maybe wait a little longer, and perhaps say a little more.

I'm sort of in the same boat with a private bank I did a 40 minute phone interview with in hopes of getting a sponsor for my master thesis, but I didn't do a follow up email to the Friday phone interview because the guy told me he would email me Monday. That was a week ago. FML.