Just bring a gallon of water and several quarts of cheap oil. Watch the temperature gauge. The 'bang' bothers me, did you fill up the AC system with 2 cans of R134a and then have the temperature go up? Happened to me, the AC system has a high pressure valve which opens with a 'bang' and then closes. Scared the heck out of me.

You have to find the source of the oil leak. A really bad head gasket will cause copious amounts of smoke out of the tail pipe. If you have a turbo, same thing if the turbo dies. The RMS leaking will leave a trail of oil under the car. Other oil leaks can be repaired. The problem with the oil sensor coming on is that is usually too late as the crank shaft bearings are without oil (usually down by 3 or more quarts).

If the engine over heated, it is possible that the head is now warped and is useless. Warped aluminum heads cannot be resurfaced because the cam journals will no longer be round and they cannot be repaired.

You need to find the source of the coolant leak and the oil leak. Only then can you decide if you should replace the head or replace the engine.

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Keeping it running is better than buying new