I would advise to play in a group, because you as a group will get more ring parts per Infernal Machine. (The chance that someone willedit for misunderstanding: You can get a ring part is higherfrom someone else's infernal machine when you play in a group than alone)
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)