Where are safe and legal places for me to start a gambling site? And what restrictions would there be. I've heard I'm not allowed to take bets from the US. But I don't know the details. Is there a website / document that explains all the details?
Online gambling is not safe from an operator's perspective - you will be targeted by criminals and by law enforcement from various nations.
Try a google search for "online poker arrest".
There are a lot of adjectives that could be used to describe the operation of an online gambling site, but "safe" is absolutely not on that list.
