For me, it’s not a number, it’s a matter of functionalities. As in, what useful functionality will I be adding to my body. In the case of RFID / NFC implants, this translates into which readers can I present my implants to, to do what, and how / how conveniently.
I’m a “low count” implantee. I only have 7 implants. I plan to add one more (payment implant) because I don’t have the ability to pay for things with any of my current implants. Other than that, I can’t think of any other transponder / body part to implant it in that would bring a new functionality to improve my life.
What I desperately need is other types of implant: visual projector, brain interface, power enhancement… Those would be massively useful to me - if they weren’t still science fiction. But as a concept, RFID gets old pretty quickly.