Q1. Is there a way to duplicate the post-upsell settings to a different type of funnel, e.g. copy "3-step Checkout" to "Intercart Checkout"?
No, you can duplicate funnels of same type only.
Q2. What happen if a customer leaves at post-upsell page, will he/she receive the order notification?
Yes, the original purchase will be completed with a delay ~10 mins.
Q3. I’ve setup everything and all funnels, is there a way to see the stats of zone & funnels?
Yes, you can view the stats/reports in Intercart Dashboard.
Q4. I can't find an option to split test discounts in post-upsell settings
Add one more product to offers for split testing (the same product is also allowed).
Q5. If we want to do post-upsells for different products, we will just use "Products to Products" and put them all under one funnel?
Yes, add multiple triggers under "Products to Products". For each post-upsell step, one offer is triggered. If you want to show multiple offers, need create multiple steps. When there's no offer triggered, that step is skipped & move to next one.