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.
The question is too generic. It is not clear what kind of background you have - are you professional programmer, building other types of sites, or you just first time thinking about starting programming. Ina second case I would recommend to start with something much less complicated like static sites..