Quick update - current thinking is to go with Aluminum standing seam panels. Painted white for optimum reflectivity.
I have obtained some more information about suppliers and will talk to them this coming week.
I'm still thinking I will remove all existing shingles down to the wood and start over basically. I'm going to do a small section myself (tear off) just to see how laborous it is.
My roof is very low slope and only 1 story so not a big safety risk. I would do the job in the winter when it's not so hot also.
We'll see.....right now though the aluminum sounds like the best choice given my proximity to the coast.
https://www.englertinc.com/blog/steel-and-aluminum-two-great-metal-roofing-materials-each-have-their-strengths/