I would like to set the location when adding the hash and automatically start (with auto-selected or all files) when the metadata has been downloaded and the pop-up received no user interaction for X minutes.

However when I add a magnet link/hash, the download path selector does not pop-up automatically, only after the metadata has been downloaded.
I have a check mark at the Settings > Transfer > General > Auto start / stop > Start new transfers.

It does that all by itself. The window only opens once the meta is downloaded, because before that it has no idea about what is contained so can't know what the files are. If the meta is downloaded and you are not present after 3 mins? it will start by itself. You need to have some settings checked off though. Under transfers/General you need "start new transfers" checked, and then in location you need to have a default folder selected.