Setup new web-site with subscriptions and Isotope-like image viewing

Ok, I'm in need of a developer to help me set up a completely new web-site from scratch. I'm NOT a novice myself and can string web-sites together no problems BUT I may need some custom development to get the specific functionality I need and this is principally where I will need a developer.

I've just bought an annual subscription to WPMU DEV and so I now have access to all those plugins & themes.

My company sells education resources. There are 2 parts to this. I sell physical products, which would need to be set up and show-cased just like any other commercial products with something like MarketPress. That's fairly straightforward I think.

The other type of products that I have are digital downloads - JPG images. These are education work-sheets that customers would download and print out themselves. I have thousands of these work-sheets spread out over dozens of categories. Each category has anywhere from 5 to 50 work-sheets. The principal requirements with regards to how I make these available are as follows:

- Customers need to be able to browse through the entire collection quickly and effortlessly without having to wait for page re-loads. I'm going for an image viewing experience that is based on an Isotope-like functionality. The idea is that the web-site visitor would browse through the collection making selections as they go as to which work-sheets they are interested in. When finished this selection process (which needs to be uninterrupted by page re-loads), they would then download them.

- I want to sell these work-sheets based on several different methods. Firstly, the user needs to be able to purchase X downloads for a fixed price. Secondly, they need to be able to 'subscribe' to X number of downloads per month for a given cost.

- Users should NOT have access to the images in high-res unless they are watermarked (it makes no sense to allow anyone to simply screen-scrape the images instead of buying them). I can provide both high-res watermarked images as well as low-res images.

My current web-site, which has a very nice theme (but is constantly conflicting with plugins) is here:

http://BounceLearningKids.com

The physical products (that would be shipped to customers) can all be found here:

http://BounceLearningKids.com/shop

The work-sheets (digital downloads) that I currently have available on the web-site (I have lots more waiting to go) can all be found here:

http://BounceLearningKids.com/worksheets

Happy to answer any further questions or provide more details. I don't have a large budget for this. I'm hoping that most of this can all be achieved simply by selecting the best plugins. The folks at WPMU DEV have suggested the following combination:

Membership
MyCred or Cubepoints
MarketPress

Your mileage may vary and I'm happy to take on any recommendations.

I will shortly have a DEV web-site where the whole thing can be put together offline.

- Chris