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.
It is not that easy to build a gambling site. You could use some premade scripts and stuffs for your casino but they are no way secure enough. Again, those will be some generic scripts and you won't be attracting many people. This is not a simple thing to do. You will have to plan and manage a lot of thing before you will be able to make something out of your casino. But then again, there are loads of well known crypto casino which means you will have to outsmart your competitors by providing something unique. There is no reason for someone to join a new casino that can not provide something new that is not available on the current known casinos.