Zen Cart Modify - coach - teach

I am a direct marketing expert (as in direct mail) moving into web. I have a client using Zen Cart that I am now responsible for web site changes until the site moves to a new platform. I am low to mid level html and php skill but have never looked at Zen cart. I need you to implement several changes: 1- will allow cart to capture coupon codes in the cart and passed through to the payment source (PlugnPay) and downloaded by ftp to import into order processing system (Dydecomp Mail Order Manager (MOM). 2- page changes to remove some discounts. I'd like to use this to have you do the work and coach me how to do it in future. Assignment may last 2 weeks - 2 months. Maybe 6 months on outside. We have graphic designer (freelance) on team. We now need a coding team member expert in Zen. Suggest an hourly rate with weekly mininum? You can see the cart and site at [login to view URL]