Welcome to the forum Polyjackpot.
Although your initiative is good for not charge any fees in the first year, but unfortunately I really doubt your project will be successful, I don't even think you can survive too. Casino is a profit oriented business, so you must have to think about the profit.
True, block hash is unpredictable - but we combine it with a server seed to avoid relying on a single source, in case one ever gets compromised.
Bets also close 5 blocks before the target, so everything's locked before the hash is known.
How the gamblers verify if your server seed were randomly generated? you might claim it's random, but we need a proof.
We publish the server seed hash before each round. After the round ends, we reveal the seed, so anyone can verify it wasn’t changed.