I'm considering a membership based system as well, it's difficult to produce such a concept for attracting subscribers. I too struggle with that.

One thing I have to consider is disk space... if I allowed video uploads, the D7 (as far as I know) doesn't limit how big it can be uploaded, does it?

Support was asked this about photo upload size for 5,000 members. The numbers presented are hard to estimate accurately but it gives you an idea.

"if every of 5,000 members upload 200 photos see more 200kb each, that will be around 95 gigabytes. ffmpeg has nothing to do with pictures, they are processed by GD Library, and the pictures get resized physically. Every image is stored in original and resized state, so, the originals are also stored. Also, every image will have a preview image (20 kb) and a thumbnail image (3 kb)."

I asked if things were resized proportionally (3x5 stays in those proportions) - "Yes!" This does make it harder to calculate, though, since it stores originals AND whatever it resizes to.

that in mind, it was only for images... now videos... oh boy! I don't even know how much a 5 minute recorded video will produce at 100% quality!

We may be talking in TBs instead of GBs.