The other permutations are wide and varied. But you obviously already know you can only have 4 Primary. In your case One of these will need to be an Extended Partition. So your next step after the above M$ could be
300GB Extended (Everything Linux in here)
2 x /
2 x /home
You can (and you should) share the home partition but you shouldn’t share home directories. So, either use a different login name on each distro or create subdirectories like /home/openSUSE, /home/Ubuntu and change the default location of the users home directory on each system.
sudo mkdir /home/openSUSE /home/Ubuntu
on openSUSE: sudo useradd --save-defaults -d /home/openSUSE