Oxygen propane, hose questions

I've labored my way through my analysis paralysis and am setting down roots on a new OP system. I'm dialed in on an oxygen concentrator, torch, mixer and tips based off or the extensive threads on this here site.

I'm working my way to the middle. I plan on flashback arrestor on the propane regulator. I know i need T-grade. I'm wondering about diameter?
-- Is there a significant difference between 3/16 and 1/4?
-- Any tips on getting from the b connector on the arrestor to the a connections on the torch?
-- Should i use check valves on the handle?

Thanks for any input.

~bob