I would advise to play in a group, because you as a group will get more ring parts per Infernal Machine. (edit for misunderstanding: You can get a ring part from someone else's infernal machine when you play in a group)

Also, since it takes time to gather the machines, it's advisable to run at at least the MP level you can farm with. 

Note that the ubers are in a narrow space (about the size of the siegebreaker area) and hit hard. I played them with a party of 2, and when one dies, the other doesn't have the time to resurrect, so either play alone or with at least 3. (Unless you're sure you won't die)