The sweet spot for a BPN is 2000, it gives everyone reading this TODAY a great chance of getting one (under 1k USD), so it'll lock up more coins early.

1000 is too low
5000 is too high

edit: with a CBX marketcap of 10M, a BPN would be valued at 20K USD with requirement of 2000 coins - that feels right for a coin with low supply getting inspiration from Bullion