the only bussinesses that make money are gambling or exchanges. exchanges have too many problems and are too big a target so it's gambling for me.
Yeah, gambling and exchanges are most profitable. But it's hard to maintain exchanges, especially if it have lot of coins listed. You would have to solve lot of support tickets, fix coin wallets and etc. Good exchange need to have lot of staff.
In gambling website it's most important to be fair and also fight against cheaters.
If I would open my bitcoin businnes, it would be online shop which sells TV's, smartphones, tablets, computers and similar stuff.