I've set both the autostart in minimized mode and the minimize to tray options, but upon autostart the window is not only on the systemtray, but also on the taskbar.
It would be nice if Spotify would be able to start only on the system tray (with a separate option, or when both of this settings is turned on).
Edit: This idea has been reposted here.
Updated on 2018-11-15
Your idea was submitted a while ago and unfortunately didn't receive the amount of kudos needed to stay active in the ideas board (100 Kudos per year).
In order to keep the Ideas Exchange clearer I'll close this idea for now, but this doesn't mean Spotify rejected this idea.
If you think this is an idea which needs to be implemented, you're welcome to post it in slightly different again :)
Have a nice day!