UmBootstrap has very long filenames for images. I can batch rename them on Windows but how will Umbraco handle that. Any tips please?

If you rename the files on disk, Umbraco won't find them any more so you'd have to update all the individual media it's themselves, probably via the database to give them the new file names. Else you'll have to re-upload all the media and update their usage.

That's the conclusion I had come to. Possible find and replace in Usync but I think I'll bite the bullet and do it manually. I was not running into all these long files names on 13, only on 14 but I think there was an update that affected both to address… long file paths. Possibly an Azure specific issue as well.

might be of interest.. https://github.com/umbraco/Umbraco.Cloud.Issues/issues/752