Check and test everything before you jump to conclusions. None of us here can tell for sure what it is.
Is all the oil milky or was there just a little gunk on the rim of the oil fill?
Sometimes if the temperatures change a lot, just humidity in general, or from lots of short trips condensation can form and cause a little waxy/milky gunk that builds up on the oil fill. It happens to my mom's Beetle, and my buddy's Xterra.
Also, check the coolant. Is there oily film/black spots in there?
I would definitely run an engine compression test and pressure test the coolant system. Before just hauling off and doing head gaskets.
To answer your questions, Fel-pro are good quality gaskets and yes always replace head bolts with a head gasket.