Hi,
Treat the application process like you are applying to a real job. Sell yourself,
What makes you the best person for the job?
Explain how you will do the job and what time it will take
Provide as much of your previous work that is relevant to the job. Show them what you can do
From experience it takes a little bit for clients to select the artist. If there is no contact with you after 24 hours you most likely wont be chosen. Sometimes they take longer but usually they would contact you relatively quickly. There have been case where a few days have passed before a message is received. If they choose to go with someone else the message will change from "not yet selected" to "declined" or "Not selected"
The models he would send you are not yours and you can't use them unless he gives his permission (usually they will let you use the work in your portfolio but not for resale).
Communication is key when it comes to these jobs. Be clear and honest when applying and you'll have a good time. If you don't do a good enough job you probably won't get paid so make sure that you can do it before applying.
Best of luck
Joe