I suggest not playing more than 15-20 minutes a day to start with, if you're feeling nauseous. You should find it getting much better after a few days, as long as you have your IPD set correctly. Just don't try to power through it in one day since it won't work and you will be sucked (tm).
I think I heard Minecrift is the best/only way to use the Oculus with Minecraft...does it work with the latest version of Minecraft? It's almost funny that a mod works but Mojang didn't do it officially, even though they were some of the earlier people getting Rifts.