There is no way to see what you are selecting as a photo in the “add to library” panel.
There are no settings or preferences to the entire software itself. Having the possibility to manually check for updates at least would be something I would consider first coding into a software that’s going public.
Not sure 100% what you mean but if you just requery a folder then already imported have a check mark and those not imported don’t…
Importing is only creating database references… files aren’t moving so the process is quick… DT does not have an auto watch sort of function but there might actually be a lua script or workaround for that as well…
What you ask for is available as greatly replied here. About checking updates, note that darktable is a multi-platform software made freely in their free time by a small team of developers. And each platform do not have same updates checking system. So what you would first consider to code is not always what is easy to code. On an open source software that you don’t pay, you will always have (and especially when all developers work on it freely on their free time) what they can and want to do.