Copper gaskets are indicated for high performance, high compression applications. If you're using a copper gasket on a stock motor, then you're creating headaches for yourself for no good reason. If you really need a copper head gasket, then you should have the motor assembled by someone who knows how to build high performance motors. No offense, but it doesn't sound like it's you. At this point you really should turn it over to someone else while there's still hope of saving the motor.

My guess about the coolant problem is that you installed the gasket wrong, the wrong kind of gasket, or your use of sealant has clogged up some cooling passages. You might want to check for coolant in your oil, and vice versa. If you're lucky, you installed a gasket without holes for all of the water passages, and substituting a correct stock gasket will take care of the problem. At the other end of the spectrum, you might need a hot-tanking and overhaul.