There are books on how to build altcoins but I don't see any in-depth guidance on how to build a gambling site.
It seems to be all trial and error.
If you know of any technique or site or forum I would appreciate hearing about it.
I doubt someone will write a book about building a gambling site. I will list out a few Do's and Dont's while building one.
1. Don't use third-party games or those shitty scripts, create your games from scratch.
2. Get your stuff developed from professional developers who have done similar work before.
3. Security/Authentication should be cross-tested with a number of tests and ran through the ethical hackers group.
4. If you don't have enough money for advertising and house, just give up the idea.
5. KYC should be remotely associated with your gambling site.