Questions about fascia & soffit repair

This is a porch roof, single layer, 54 year old house. Started tearing off rotting fascia and found a sub-fascia rotted as well. Also took off soffit in that area. All the rot is at the end, by the fascia. Pic 1 shows rot (NOTE: oddly, the soffit and gutter of the house (upper) roof showed up in the pic and it looks odd, so I labeled it so no one gets confused (just ignore that part). I looked up into the roof and most of the sheathing is good, except the last 3 inches–some parts have rot (pic 2 shows this). Noting is moist–the sub-fasica & fascia rot is bone dry.

[edit]: Perhaps a clue to the original problem: I just examined the removed soffit and it had about 6 inches of black on it and that part was dirty. Maybe water sat there?

First question: what caused this? I’d like to know in case there’s some other repair I need to do. Because it’s bone dry, maybe the issue was addressed at some point in the past?

Second question: the porch roof is cupped a bit at the end where the gutter was. Once stuff was removed, I confirmed the sheathing appears to have rotted at the end. I plan to roof next year. Is there anything I should do about this NOW (maybe before I put new soffit, sub-fascia & fascia on)?

Third question: The horizontal parts that the soffit is nailed to (see ‘?’ in first pic) are loose–I can rotate them a bit by hand because they only have one nail at each end. Is this an issue? I don’t think so because they seem to be only there to hold up the soffit, but since I’m here, I’ll ask.