Suppose If I am going to use the offshore server for hosting my hidden service .onion domain, then my private keys will be on the remote server. Well, that means the host can impersonate my site or hijack it later. How can I protect the ownership of a hidden service?
Either host with a company you truly trust it will not steal your private keys, or if you are too paranoid to trust anyone, host your hidden service on your own server. For the latter option, you need a computer connected to the internet, with Tor installed and web server such as Apache (or whatever you need) properly configured with the hidden services .onion domain.