Well, recall that Gallery uploads photos such that the *Apache* user owns them, so the photos technically wouldn't infringe on your space quota... Just don't tell your ISP that :smile:
With NetPBM and Jhead binaries, Gallery has about a 2.5 MB footprint. The space the photos takes up depends entirely on the size of your individual photos. I have 1700 digital camera photos on my gallery, all about 640x480 and they take up about 200 MB of space. 50 photos... maybe between 5 and 10 MB? Again, it depends on whether you build intermediate sized photos and how big the originals are.
Gallery 2 when released will use MySQL (or perhaps other DB interfaces too) to store its data, though the photos themselves will still be stored as files, not in the DB itself.