Wotcha and welcome - sorry your introduction to the forum is under these circumstances
It does sound like the head gasket has gone, the oil in the coolant may have something to do with the level however it may be symptomatic of a cracked head / liner and oil is getting into the system that way.
You mention oil temp guage - do you mean the one on the dash by the rev counter / speedo, if so Im pretty sure this is a coolant temp guage and would shoot up if there is limited coolant going around your system, there may be an air lock or also the thermostat may have failed which would stop the flow