Reasons number 1 and 2 why I don't like to use copper head gaskets. They just like to leak and unless the water passages are identical to stock they tend to overheat. For the leaking problem use the grey Yamabond non hardening epoxy smeared on both sides and let dry to a tacky condition. It is the best sealant available for copper head gaskets. Honestly the best solution is just go with the oem head gasket unless this is a race only car which it doesn't sound like.

There is also a bleeder valve on most recent years of the honda/acura water outlets. You must bleed the system until you get all air bubbles out or else the air pocket will make the sending unit not read correctly and may not allow the thermostat to operate correctly.