Math fact website

I want to create a website where students can take timed math fact tests in the basic operations. Paid version of site will allow teachers/parents to create student accounts that can track students' progress over time. Looking to create badges/awards that reward kids for their progress as well. Want a seamless payment setup where accounts can pay via paypal, automatically be activated, and can begin without delay. Looking to pay $10-$15 per hour but would want to set up a general estimate of # of hours expected for this project to take ahead of time.