Unless you’re using the TOR Browser or Mullvad Browser, you’re already fingerprintable with a high degree of accuracy for those determined enough. If you’re that worried about fingerprinting, you should probably be using one of those.

There’s no magic number of extensions that would be considered “safest” from a fingerprinting perspective. Any you add will likely adjust your fingerprint in its own way. But as I said, since you’re probably uniquely identifiable anyway you can’t really get “more unique.”

With that said, it’s best to keep your extensions to a minimum for other reasons too. Each extension represents an increased attack surface and you have to trust more developers to not be implementing exploitable code directly into your browser. Generally, I find UBlock Origin to be enough and maybe an extension for your password manager or a few other things. I don’t generally run more than 5.