Advice wanted on new site

Hey everyone,

I hope this is the correct place for me to be posting this

I am setting up a new site, and have a few particular requirements, and was hoping I could get some feedback as to the possibilities of this?

Before I go ahead, I will state that i am aware of zencart, which I am looking at using. However for the purposes of simplicity it would be nice to stay exclusively within gallery2, using cart, zipcart, and paypal checkout. As such I am wondering if it is possible to use the above (less zencart) in combination for the setup below. Thank you in advance

The wesite's user experience will be;

A web site hosting 5000+ images.

Without login, users may see a low res version with a watermark. With login, users may see the same resolution, however without a watermark.

Individual hi-res images may be purchased via a zip download, through paypal. It would be desirable if people could purchase images in the following brackets with different rates for each; 1-20, 21-50, 51-100, 100+.

Categories and sub-categories (albums, sub-albums) should also be buyable at a bulk rate.

The backend will be;

Bulk image upload based on folders, with automatic resizing for various user logins and for purchaseable option.

Thank you again!
Crix.