I run a 12.5" switchblock Noveske upper. It runs well on everything I've fed it, including bags of mixed up cheap stuff. Its accurate too!
It's long enough keep decent ballistics. Also, I like 11+ inches to stabalize the round, reducing baffle strike.
Yet, it's short enough to be handy even when suppressed.
The switchblock works. I like that you can turn it "off." i.e. single shot only.
I use a Gieselle SSA Trigger in this lower and like it alot. I also have a Timney 3lb single stage in a Mk12 Mod0 and like it just as well. The Timney has better feel but it clearly strikes a little lighter. FWIW, I run AR Gold in my target AR and it's got the best feel yet. I do have a KNS anti walk kit on the Timney.
My experience with LaRue is good as well.
If I were going to "Piston" an SBR, I would choose PWS. Based on theory and second hand knowledge only. <-- grain of salt
I think your setup sounds good and well thought out.