Danno...

Amazon for the gasket kit. Hands down. No questions.
Use ARP head studs if you are doing HG's
Oil pan, if you swap from steel to aluminum, yes change the pickup tube as well.
I assume you are using a Gen V charger and the DBW TB, so that's easy.
Swap evep and fuel rails over as well. (evap is on the charger)
Remember the ECT is most likely different, I'm not sure which year that changed, but it changed.
Flex should be fine, but I'd use the L32 dual drilled one.