You can issue an Asset for the ingame currency. NXT would be the largest denomination that would also be in the game for the big treasures, but for most common use it could just be the Roobles. If you want the Roobles to float in value against NXT, then just let the Asset Exchange do its thing. If you want it to be tied to NXT, you can just put bid/ask at a fixed exchange rate.

Also, I dont see why to limit to a single game. Games are BIG! I suggest keeping track of all the ideas and start with the fastest to get working. Doing something simple is a great learning experience. Then the second game becomes more ambitious, etc.

James

P.S. Please keep track of all the donations that come in for this, I have a feeling the total will become quite large, especially if you offer ingame Vorpal swords to big donors