osCommerce site with credit system similar to istockphoto for downloadable music resources

The site is a subscription site (a music club) for churches/music directors who need fresh material to teach their music departments. I built a site with RapidWeaver that worked OKAY, but I'm I don't consider myself a web designer (let's just say I'm not adept at Dreamweaver), and in order for me to market this on the level that I would like to, I need a much better and more efficient web presence for this. Here are the present requirements: A credit purchasing system whereby customers can purchase credits (similar to iStockPhoto) and use them for whatever product they choose. Monthly subscribers will receive credits at a much lower rate, but non-subscribers can also purchase (although they will need to set up a free account). I currently use Paypal's Web Payments Pro for payment processing. It seems like an osCommerce solution with the points-rewards module or the credit class and gift voucher might work best for this. Automated delivery of secure download links via email or a secure page. I've been using Vibralogix's Linklok IPN and been playing with Sitelok from them, as well, but haven't implemented it yet. I'm okay with using that, but I'm also open to other ideas. A site that can be changed/added to on a regular basis (ie. monthly). I have seen some oscommerce template sites that COULD be customized to work like this, but I don't have the time to figure it all out. Needs to be finished by June 15, if at all possible. I will give the necessary design concepts (even go so far as to design the overall look in Photoshop) and answer any other questions.