VPS or dedicated server... It seems that  raspberrypi 3 is not as powerful as these
Btw, is it safe to put everything on a VPS server? I don't trust any big company at all.

I expect we will see some experimentation and over time our concept of best practices for providing signer security and availability will evolve.

I will just outline what I had envisioned with the expectation that the community may be able improve upon it.

First, remember that no one needs to know signer IP addresses at any time. Communication to signers and from signers is exclusively by general network broadcast among all peers. Allowing anyone to know the IP address of a signer client is an unnecessary security risk.

With that in mind, signers can open a single use email account and purchase their Linux VPS or dedicated server using NuBits or Bitcoin. They then install the clients they need (such as Nu, B&C and Bitcoin) and the Tor Browser Bundle. The clients are all easily configured to use Tor as a proxy using the graphical interfaces.

The B&C network is unable to distinguish a signer node from other nodes that are minting or just broadcasting messages. Even if you could identify a signer node, you would only know the IP address of its Tor exit node.

Though this setup brings some risk of compromise from the VPS service provider, it seems quite small because there is no reason they would understand the VPS is being used for B&C Exchange signing. VPS providers compete on providing computing that can't be tampered with by employees with administrative rights. All the VPS provider can observe from the network traffic is that the server is communicating over Tor.

It is possible to increase the security of the design by using multiple servers, failover nodes and so forth, but the above configuration is quite simple to set up and should suffice to begin with.

A signer server set up this way is likely harder to locate than a Tor hidden service.