Stability and finish are two different things. Mid forty temps to high eighties and 90? Same thing. Sunlight with no over hang on the exterior for shade? A finish killer and constant maintenance and vigilance .

A client of mine invested 40 k in a custom wood door. Black /painted. Western exposure. Result? Cracks. Everywhere.

All solid wood doors are a TIME and money COMMITMENT. No matter the species. Even teak. Perhaps contact this guy : )

https://en.bovalls.com/maintenance-installation-2/maintenance-and-care-of-teak-doors/

Things to remember

The treatment of oiled exterior doors never finishes, they must be maintained in order not to become discoloured and unsightly but also to prevent them absorbing moisture and then swelling. If the wood dries out, it absorbs moisture and swells. This can cause the door to bend, which in turn can lead to problems with both tightness and closure. Depending on the location of the door and the climate, the door may need to be oiled several times a year.

We also recommend that you add an extra layer of oil to the door once a year. Remember that you should apply oil at a time when there are no mould spores or pollen in the air as these get stuck in the oil. So do it in the early spring or late autumn.No amount of metal will change the protection factor.

"When is it even more important to maintain your teak doors?
Doors in locations without a roof are particularly exposed - especially in coastal areas. It is also even more important to maintain doors facing south and west. The most vulnerable parts of the door, such as the lower edge of the door where water splashes, may otherwise have a different colour tone than its less exposed parts.”

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1) if adding metal strips to the solid wood will provide weather protection

??? Like a kick plate? No, a kick plate won't provide protection from the weather.

Lots more to it than temp & humidity. Biggest being the exposure. Sun, rain, weather side of the house (prevailing direction of wind, storms), under a porch or not, depth of eaves, guttering... "Solid wood" of what species? Really solid, solid wood or veneers over some 'wood' composite core?

Hands down best protection for an exterior door is a storm door.