how to set up ssh authentication for dedicated ip

Can you explain what you want? ssh login for non-ssl doesn't make a whole lot of sense.

Which IP is dedicated, the client or the server (I assume you mean client if so just lock the ssh port down to that ip using iptables).

SFTP comes with SSH by default.

Use tcpwrappers like:

/etc/hosts.allow > here you would append wich address has access to specific app

/etc/hosts.deny > here you would append wich address has not access to specific app

Regards