I would save the PP SN+ oil for the Turbo only.
I think you said some of your PP score was SN, so just alternate MS5k, PP SN, and MSS.
If the MSS is SN+, then I may use it in the Turbo, depending on how much of the PP is SN+.
As for shelf life, that gets brought up all the time.
A few manufacturers give a 4-5 year life, but Valvoline says no expiration date.
The only real issue is making sure that the oil your using meets the spec of the engine you are using it in, and many will say shake the bottle up before using.
I have a good 5-6 years worth of oil (if I can quit buying it), and have no concerns since I have no plans of getting a vehicle in the next 10 years that needs more than SN oil.