The old coat of solid stain that has weathered makes a good prime coat if it's clean, dull & dry and is a sound coat, meaning not peeling or compromised in some other way. Duration is a house paint, whereas the other is a stain. The chief difference is the dry film thickness and sheen. the thin dry film makes the stain follow the contours of the wood and can give you a more authentic or maybe even rustic look, depending on the wood. It will almost always be flat, with no shine at all. The thicker coat will more fill in the grain of the wood and probably have an eggshell or higher shine, maybe even to a satin or semi-gloss. It most likely will not be available flat. A thinner coat means shorter life, the trade-off reflected in the price. A properly applied thicker coat of duration can be expected to last a good long while, but I wouldn't use anyone's "lifetime". If the wood has roughness or character to it, that you want to exploit for a certain look, I'd put stain on it. If the wood is smooth, almost shiny the way it is, I'd use house paint.

I've been looking at high end roofing tile websites and one of them has a color expert that made recommendations for house paint colors with their orange/brown roof tiles. Here is a link to some of the schemes they recommend that may give you some inspiration: https://www.davinciroofscapes.com/blog/exterior-color-schemes-autumn/ You can color match to Sherwin Williams brand paint.

Celery- That color was actually on my list and then for some reason I didn't get a sample of it. I didn't know gray was going out already! I do have Patricia- I live in a teeny little neighborhood with only about 6 houses and two of them have a greenish tint that I am not fond of. The thing is I have a weird tan/brown stone to my house so going sage would probably match better than the blue/gray anyway. We had some storm damage and my roof is now moire black from certainteed. It's definitely a strange looking home but the inside is what sold me on it. Honestly I feel like there's not much hope for curb appeal. I was going to go vertical board and batten style for the hardie board but clearly I am clueless if anyone has better advice I would very much appreciate it!

Sherwin Williams can color match it for you. It may be a tiny bit different than the original due to pigment differences, but usually it’s not enough to be noticable once up.