Hey there, congrats on the Z6 II!! I literally just went through this same thing upgrading from my old D750, so I totally feel u. Honestly, unless youre doing heavy video, you can probably just stick with a fast SD like the SanDisk 128GB Extreme PRO SDXC UHS-II Card for now to save some cash. I mean, the CFexpress cards are fast but man, they’re pricey! Definitely grab the Nikon FTZ II Mount Adapter if you have glass you love, it works basically perfectly and saves you from buying all new lenses at once. Also, you lowkey NEED a spare Nikon EN-EL15c Rechargeable Li-ion Battery because mirrorless batteries just dont last as long as DSLRs. It’s kinda a learning curve but sooo worth it once you get used to the autofocus... let me know if you have more questions!! gl!

TL;DR: Get a CFexpress card for the buffer and an L-bracket for better ergonomics. In my experience, you should just bite the bullet on the storage. While SD works, a Lexar Professional 128GB CFexpress Type B Card makes the camera feel much more responsive. The buffer clears almost instantly which is a godsend during any kind of action shooting. Also, coming from a DSLR, the Z6 II might feel a bit small in the hand. I've used a SmallRig L-Bracket for Nikon Z6 II since day one. It gives your pinky a place to rest and makes vertical tripod shots a breeze. One last thing... skip the cheap screen protectors and get the Nikon LPC-Z6 Glass Screen Protector. It fits perfectly and doesnt mess with the touch sensitivity like some of the generic ones do.