Unfortunately I wasn't able to get a interface to appear

Actually I did manage to get an interface to come up, with the KVM interface model=e1000
But It wasn't functional under junos for some reason

It seems that junos has a watchdog and it could also see issues Em0 is the interface name under junos, i dont know why its called em0 though, it was also called em0 under vmware when i tried in the past.
I thought e1000 works with like everything...

KVM in routerOS is not the newest relese and virtualized hardware might be not on par with drivers in JunOS. There is other interfaces available, you can try those.