Hi there,
loads of questions you have there. That is probably one of the reasons nobody answered them. Maybe also the fact that you went to a Reality Capture forum to then say you do your photogrammetry in agisoft metashape.
The only thing I can answer here is the high ISO question. I made some tests about it myself some time ago and found, that it isn’t a good idea. Reason being, that no matter how good or smart the denoising is in any of the apps (Lightroom, Topaz Labs Denoise AI, ect.) no software is clever enough to only remove true noise. They all also remove features that where actually not noise. Because of that you actually blur your images slightly. I fould that comparing the same scanned object with ISO 100 vs. IS) 800 or higher and denoising always resulted in the ISO 100 scan being much better. The textures alone where a lot better, since I didn’t have to “blur” my images to get rid of the noise.
It simply isn’t worth it if quality is what you are after.
I also don’t recomend delighting textures of scans done in direct sun light. I used agisoft delighter in the past, and it does a fairly good job, but if the shadows are too dark, i.e. nearly black, then the resulting texture in those areas tends to suck big time, as there is just not enough information left in the shadows, for the software to be able to bring back the details. So if possible, do not shoot in direct sunlight.
Cheers
Guillaume