IIRC when Eric created and launched moneypot his bank roll was around 80-90 bitcoins and that was enough. I remember him saying it was nerve racking the first few days when he went to sleep wondering if someone would bust his bank roll by the time he woke up.

What you could do is limit the max bet size if you have a smaller bank roll, but don't make it too small or you'll lose potential players.

As for legality that's a huge gray area and a risk.

Good luck on your project.