There is an even more relevant video of using external storage trough USB. He recommends using software raid:

Can We Build a Home Server Out of Mini PCs?

It is possible, it’s just not generally supported be ISP routers. Also there is a possibility of performance issues since IPv4 NAT often relies on hardware acceleration which might not work for NAT6.

Even tough IPv6 is technically superior to IPv4 for the network operator it doesn’t have clear benefits for home users.

Having global addresses instead of NAT means less control over your LAN and these unique public addresses can track users more accurately.

There are some used options e.g. 5700 XT-s are really cheap because many of them were mining card. For new cards there aren’t many options RX 6600 has relatively good value, but it’s only worth it if efficiency or features like hw video codecs are important for you.