DIY Metal roof installation

I recently purchased a double wide manufactured home. I knew going in that the roof would need replaced in the next couple years and I am thinking of going with metal and doing it myself (with the help of some friends) I don't have any roofing experience but I do have some carpentry experience and I'm pretty handy. I have a couple of questions to get started. I don't know the exact slope of the roof, it is pretty shallow, a typical double wide with a small front porch gable. It already has 2 layers of shingles and I know there are some soft spots in the decking that will need replaced so I plan on removing all shingles, replacing and reinforcing the decking, as well as adding a ridge vent (now I've only got 3 or 4 roof vents and I've been told that is inadequate. SO my quest begins. Where do I start. I know I want some sort of water/ice barrier instead of basic roofing felt. I've read that some people install wooden strips to fasten the metal to where as others have said that steel has condensation problems and it should be installed flat against the decking. What are the thoughts on this? Also, the actual installation of the panels themselves seems pretty straight forward but what about at the edges, valleys and ridge top? What special pieces do I need for that. I can get the panels at my local big box store but they don't carry any specialized pieces. What else do I need to take into consideration? Is this even something I should attempt as a "DIY" project or will I do more harm then good? Thanks in advance for any info.