2006 Chevrolet Equinox Engine

I was driving my 2006 Chevy Equinox and the engine light flashed on and went off. Then my coolant light came on and I was all the way in red. My car has never overheated before. Sometimes while idiling for long periods the temperature would go up but never more than the half way mark on temperature gage. I pulled over and turned the car off. My coolant level was where it should be and there was nothing smoking. The fans continued to run after the car was shut off for longer than normal. I waited about 5 minutes and turned the car back on. Right when it turned over there was a big poof sound and there was a large amount of thick white smoke that shot out of my tailpipe. I turned the car off and opened the hood. There was a small amount of smoke coming from the passenger side of the hood but it was gone by the time I popped the hood. I checked the coolant level and now it was completely empty. I called for a tow truck and did not attempt to start it back up. I did check the oil at the time this happened and it was NOT milky. After the car was on the tow truck there were a few spots on the ground from under the engine to the backseats of coolant. The next day a friend looked at it. We put water in it and started it up. The car did start and was running. There was smoke coming from the exhaust but not a lot. We did not drive it but let it sit for about two minutes while running. I kept my eye on the temperature while it was running and it never went up like it was getting hot. We turned the car off and checked the oil and this time it was milky. I had it towed to my parents mechanic who suggested I buy a used motor and put in it because the head gasket was blown. I had called around a couple of other places and some said intake gasket, head gasket, or busted radiator hose somewhere or an exhaust issue. What are your thoughts.