Excellent choice of a first project, nice work. I had planned to do this exact thing if someone else didn't do it, so when it gets too hard for mortals to generate 50BTC, new users could get some coins to play with right away. Donations should be able to keep it filled. The display showing the balance in the dispenser encourages people to top it up.
You should put a donation bitcoin address on the page for those who want to add funds to it, which ideally should update to a new address whenever it receives something.