Generally there are no real problems. If you're fine with mostly stock AOSP, you should be fine with GrapheneOS.
If you use Google Pay, you're out of luck. There are alternatives for that depending on where you live though (mostly in Europe, in the US there's no other option AFAIK). Rarely an app won't work, but usually fiddling with some security settings for the app will fix it. Very rarely an app won't work at all because (like Google Wallet) it uses Play Integrity and requires a level that requires Google to certify the OS.
Pretty much the only thing I miss is the ability to do NFC payments.

They'd work. You might need to install play services for those, not totally sure (Google has shoved an annoying amount of functionality into play services). NFC itself is functional, but various apps that support NFC may not work because of Play Integrity.