Props (traffic variables) are hit-based, not persistent, so they don’t carry forward like eVars. Props are useful when you want pathing analysis.
With Setup 2 you ensures that each ecommerce milestone (Product View, Add to Cart, Checkout, Purchase) carries all relevant eVars — so even if persistence expires early, you still capture the right attribution.
Setup 1 is not ideal because it bloats every pageview unnecessarily and doesn’t leverage ecommerce rules properly.
Setup 3 is feasible if eVar expiration and persistence are carefully managed to ensure earlier attributes carry through to purchase, but it prioritizes lean payloads at the cost of more complex debugging and reporting.