If it's leaking at the head gasket, it's not holding compression (hence, the hard starting and inability to idle).
As to why the gasket blew..well, you said it hasn't overheated. Are you sure?
Nevertheless, I'd pull the head off and take it to the dealer or a machine shop. The machine shop can tell you if the head is warped. If not, put a new gasket on it and torque it properly!!!. You'll have to re-torque after so many hours (you really need the shop manual for this). If you don't know what proper torque technique is, let the dealer do the job.
If the head is warped, you may have to strip the head down to a bare casting (leave the valve seats in though). The machine shop can mill it flat for you. You want the minimum amount of material taken off..or whatever the shop manual requires. There may be thicker gaskets available to account for the material removed from the head (if it comes to that). This is to maintain the correct compression ratio.
By the way, when you pull the head off, look for cracks around the head and block. If you seeing oil, the crack may have started at one of the oil passages. Cracked heads can be welded, but if it is cracked (and I hope it isn't!!!), you might want to start looking around for replacement parts. If the block is cracked (unlikely as it is)...that's beyond my realm of expertise.