How good is ATECC508A as a cryptographic token?

[technix]

In a nutshell, this idea would be building a YubiKey clone of my own, since I have trouble buying YubiKey legitimately in China (due to US export controls.) The centerpiece of the token would be an ATECC508A chip.

Questions:
1. How good is it? As in how secure is it?
2. Is there any standard USB protocol for security tokens like this? Hopefully this standard protocol will allow me to log into my computer using this.
3. Do I need a PKI to use it, or can I just rely on decentralized crypto like GPG?
4. Recommendations of the fingerprint scanner? Or do I even need one?
5. Is it a good idea to put the PCB assembly in a dremmeled USB stick case?
6. Is there any good solution for storing and sending sensitive data secured using such tokens? (If GPG can work, this is a no-brainer as it supports both file encryption and S/MIME with PGP. Otherwise...)