> Will for example, 1.1.1.1 still resolve my domain correctly, even if my providers nameserver is down for an hour?

1.1.1.1 is virtually impossible to DDoS, because it’s anycasted in _a lot_ of places, and Cloudflare has the capacity to mitigate the largest of DDoS attacks.

> - Is it a good idea to setup my own nameserver which basically just "copies" the entries from my current provider and specify it (wherever that may be). By doing this I won't have to maintain 2 different NS, only the one from the provider since the 'secondary' will simply be a copy of the primary?

This would be a caching NS. It's not a bad idea, especially if it can automatically forward to a different service provided one is down, but you might as well just use 1.1.1.1. I've never seen 1.1.1.1 down.