Coin Dropper asked how much money is needed specifically for the
bankroll, so I'm not sure why everyone is speculating about licensing, development and marketing costs.
Assuming you don't want to risk more than is mathematically optimal, you can calculate the required bankroll for a dice game depending on the most you would like to allow players to win in a single bet and your game's house edge. For example, to offer a maximum profit per bet of 0.5 BTC with a house edge of 1%, a bankroll of 0.5 BTC / 1% = 50 BTC is necessary.
People say this formula is solid, but isn't it supposed to depend on the number of users somehow? Surely we have to set limit for a maximum bet amount, but if we have 10 players on the website and one of them one on a 10% chance then it's one thing, while if there is a hundred players, then the potential win is bigger and the bankroll is supposed to cover it. Yes, we can expect that more people means more money waged and often lost, but probability can be tricky and one might on the early stage of casino's development suddenly get lucky, no?
No, as long as the maximum profit per bet is never exceeded, the number of users doesn't affect the risk to the bankroll. From the perspective of the house, it just receives bets one after the other. How quickly those bets are made or from how many players they come doesn't matter. Since the optimal risk is relative to the bankroll, the house is guaranteed to never risk too much, even if players are lucky.
Restricting the maximum bet size doesn't impact the expected bankroll growth either. For example,
bustadice allows wagers of any size that don't attempt to win more than the maximum profit. If you wanted to you could place a 1,000 BTC bet and it would be perfectly safe for the house to accept.