Thanks for all the replies JewelsProject and Pro4Never.
A few more questions and remarks for the road. I prefer asking them here so that everyone can catch up with the replies.

Gambling
Have you checked what are the regulations regarding gambling in your country?
If your country has gambling regulations, it wouldn't be a good idea to host the gambling aspect of the game on servers under your company's responsibility.
There is an easy way around though: Ethereum smart contracts. If you have the gambling process run as a smart contract on Ethereum, it's not anymore under your responsibility but that of the network at large that is to say everyone and no one, but you can still get a cut from "the house"'s proceeds as a "shareholder" of the smart contract. For that to work best, I would recommend to implement Jewels as an Ethereum based tokens. You could also sell "The House" tokens if you want to share the costs, risks and rewards of running the gambling smart contracts.

On-chain game assets
If you are really motivated to make a kick-ass game economy, motivate other game developers to join, and get a lot of attention in the crypto community, you could allow game items to be stored on-chain and exchanged as crypto tokens. Maybe not every item, but at least legendary items. You could create new "collector" items once in a while, give away half of them at random in the game, and sell the rest for Jewels. Makes another nice source of income. That's exactly what Spells of Genesis is doing. They are using Counterparty tokens to represent each type of tradable card, and they are exchanged for their currency called BitCrystals on the Couterparty decentralized exchange. Of course if you are using Ethereum for gambling, it would make more sense to implement that using Ethereum tokens. In that case, you could simply fork the EtherEx exchange contract and make an in-game asset exchanges you control (in which case you can also charge trading fees, which would be another revenue source).