How much investment is needed to form a fully functional bitcoin based gambling platform?
Depends on the number of games you offer.And obviously the investors you have on the house.Can't give you an exact figure but 50 bitcoins will be a good number to start with.
Is it possible to create the complete platform individually without the help of software providers? How much coding is required for that?
How much ROI should I expect from a casino?
Yes it's totally possible to create your own casino from scratch without the providers. You will have to hire good developers and that would cost nothing less than 50k because you will need a team that would create design,develop it and also handle security side of the things.This is subjective depending on the level you developers you want on board.
The ROI depends on the number of players you manage to bring on the site.
If there's anyone already running a gambling business or anyone who has information about this topic, can you share your insights please?
What you want to know ? Better invest in a good casino rather starting your own stuff if you don't have the required money.