We can give You a solution like this:
(1) Users just upload files and send links, Members sign in and upload files then send a links for whom ever he like and create e-mail listings with categories to proceed his new upload to predefined groups and price also like member but extra he can browse his files, edit statistics of downloads per file, open or delete his files.
Banner management can be configured to show banners randomly on same position with multiple heights but same width or inverse, what depend of position of banner. Banner management also have statistics of wieved and clicked and can be limit by duration of time, per number of clicks or views. Banner management can also set border color. Formats of banners are .gif, .jpg and flash. You can upload them and set all caracteristics through internet browser.
Solution of downloads You mentioned is ok, reset numbers of days left to show file for download.
Administration of all section of web is through internet browser, user friendly.
We are group of one designer and two programers. Solution will be ASP Vbscript and MSSQL server. For me it is the most likely combination. Thank You very much!