In my opinion, keep it pretty low until you build up a larger audience, but for now if I were you I'd format it like this.
1. Intro
2. Sponser #1
3. Show Content, Interview, etc.
4. Conclusion, Upcoming show info, etc
5. Sponser #2
Don't start mixing in advertising mid-show until you've built up more listership, in which case WMR might come knocking on your door anyway.
Also, a piece of advice: don't just be another shoemoney-esq interview podcast... That gets dry rather quickly. Try to keep it fresh with original content and limit interviews to maybe every other show.