Foam over existing metal roof

i have read about every topic and even called two manufacturers but have always gotten contradictory information on this topic. Here is my specific scenario: I have a 100 year old home in VA with a mechanical seam metal roof. it is installed over what i will refer to as purlin decking for lack of a better term. The purlins are roughly 1x4's space about 4 to 6 inches apart. the roof is a 8x12 and the house is what i call a 'cape cod' and by that i mean it is a 2 story house with the 2nd story rooms surronded by attic space ( a triangular space above the ceiling and triangular knee walls on both sides. i would estimate that roughly 50% of the roof area sits overtop of 'cathedral ceiling' style walls where the wall is composed of metal roof => purlins =>2x4 framing with blow in cellulose => original tongue and groove wood walls. The roof is leaky and needs to be replaced. I am trying to determine the best way to proceed. It seems my options are 1) remove the old roof and get a new one put on directly over the purlins 2) hammer down the roof seams and add foam insulation between horizontal sleepers directly over the exisiting roof or 3) remove the roof, add plywood sheathing, add foam, add another layer of sheating, then the metal roof. Of course option1 gives me very little R value in the roof and option 3 is much more labor and material cost. Is option 2 a bad idea or would it work? will vapor build up under the 1st metal roo? what do i need to watch out for? the existing roof is framed out of rough sawn oak 2x4s, would the added layer of foam and 2nd metal roof cause a weight issue? I should add that the eaves are not vented as it is a stone house and the stone extends all the way to the roof 'deck' so please consider that detail if it makes a difference. Please Help!! Thanks so much!