In my opinion, all enhancements can be in same package.
Enhancements 123 need to be in subpackage, and 45 in another subpackage.
If package is not assigned to switch, subpackages can be assigned to separate switches.
I am looking at diagram in this link. (I haven't tried it though).
http://help.sap.com/saphelp_nw04s/helpdata/en/42/f186d1faf93255e10000000a1553f7/content.htm