It shouldn’t get duplicated, the latest update to B1357 was supposed to fix this
As for autoquitting the server, you can’t. There are many advantages to running the server as a separate process, as laid out in the thread linked below. And I can’t think of any disadvantages to have it running when you don’t play Roon - as its inactive, the operating system should swap it to disk in the event of memory pressure and it shouldn’t be using CPU in any noticeable way.
I guess if you really want to you can find a way to autokill it
Depending on your operating system, there are ways to setup a batchfile/script to shut down Roon and Roon-Server which can be executed from your taskbar/finder - Google is your friend.
I assume you mean the icon is duplicated. Sometimes background apps can leave icons behind, even if they’re not running anymore. If you hover with the mouse over the icons, the orphaned one should disappear.