re-roof

Hello, I am looking to get some feedback and or input on a residential home from the 70’s. I have a home that was initially a summer cottage and is now lived in year round in Wisconsin. So the concern is that the home is under insulated on the roof. The shingles are respectable, but the heating and cooling bills are “out of the roof”, literally! The current materials present are five 4x10 beams which run horizontally the length of the house, and 2x6 T&G that runs vertical on top of the horizontal beams. Inside the home is a cathedral ceiling throughout, so no attic space or insulation inside, the 2x6 T&G viewed from inside is also the roof planking. On the outside is 1” rigid foam, felt underlayment and asphalt shingles. I would like to add R value with 3 or 4 inches of rigid insulation on top off existing roof. I have done quite a bit of research and believe the extruded closed cell polystyrene would be the way to go, which would get about R5/in. I would also like to avoid tear off and try to use present materials to help with R value, have less clean up, and not have to worry about timing and weather. Also, it seems that venting between top of new rigid insulation and new roofing material would be best practice to avoid ice dams and bridging, creating a “cold roof”. So far the plan would be to run 2x4’s flat 24 in OC vertically on top of rigid foam, then put down substrate, and new roof material. Venting would be from soffit to ridge. Another question revolves around new roofing material. I would like to go with metal roofing, probably standing seam. I am trying to decide if I should go with a solid substrate (5/8 OSB), or flat 1x4’s every 24 in OC horizontally as battens, either would lay on top of flat vertical 2x4’s used for venting. The home has large overhangs on all sides, 43 in @ the eves, and 50 in @ the gable ends, so I was planning to only add insulation over the living space and block up outer perimeter with lumber to match same height. So the question is if there should be concern for shrinkage and changing thickness over time on the area with rigid insulation, versus remaining perimeter spaces that will hold size with built up lumber? Would there be a need to put roofing felt or a barrier over existing shingles before putting rigid insulation down? If bats are used 24 in OC, would there still be a need for felt between metal panels and battens as a slip material? Lastly, would I need 30lb felt over rigid insulation to protect from condensation from underside of panels? In conclusion, after consulting with several roofers and insulation companies, it seems that this is a unique situation, and each has their own Idea and approach, which is kind of scary. Thank you ahead of time, I do realize some of the questions have been posted and answered many times over, as I have seen through the posts, I am just trying to provide a good description and not miss any important steps on a hopefully “lifetime” re-roof. Roof is 3:12 pitch, location SE WI, roof panels aprx 16’5” Thank you for your time and consideration, I look forward to your reply Concerned homeowner TK