In a nutshell: is DHT [always] public?

I would create a “personal” dynamic routing system using IPFS’s DHT.
I just need to be sure about some things:

  • The DHT is unique o I have to create a private one on my server?
  • Do I have to provide an uptime-stable daemon for ensuring the distribution of these values? Is this daemon the technically called “IPFS node”?
  • There is a yet implemented a sort of method that through a private and public key ensures the fact that a value is created by my service?
  • The key limit is 256 bytes, right? There are disadvantages to use a longer key rather than a shorter one?
  • Can I correctly take advantage of expiration for updating a key value?

Thank you!

Ok, I’m progressively studying IPFS: the community it’s almost dead, but the APIs is rich and the documentation it’s pretty wide, though requires keywords knowledge and a little of insight.

This is the url for the common question “how to update a published file”: