The oil in the catch can is because of problems with the way the nipple comes off the valve cover and baffling. If you can create a bit more of a rise and/or pull from the top of the nipple (maybe add some of the fibre netting stuff) so that oil has a better chance to flow back it will help. Of course the flow you have from vacuum leaks(eg. rear main seal) and blowby the more the baffling problem shows up. Think of it as the catch can is supposed to be in the valve cover. The stuck rings I think can be helped by using premium gas and some aggressive driving. Works for me!
The catch can is a good idea for checking on how the system is working but you shouldn't need it when you have things working reasonably well.
I can see only using one port on the vacuum manifold being a problem as well but not so much for your oil in the catch can.