

If there isn’t a written down set of features, it sounds like they want you to get done with as much as you can for less than $100,000.
That’s going to require more coordination in your end, since it means holding their hands while they prioritize what minimum features they can accept.
Linux keeps getting more development because it is the cheapest way to develop a platform. It is the reason why almost all servers are Linux and it was used as the basis for Android.
That said, Steam is a wildly profitable company that is self aware enough to not kill its golden goose.