If Im renting my storage on the Sia network, is my IP address visible? Like not only for the people who will rent it but also for the public?
Yes your IP is public. It is info submitted to the blockchain at the moment you announce your host, and it is in the hostdb file on every Sia client. In every P2P network, IPs are known by the rest of the peers
If it was not public, no potential renter could ever reach your host to make file contracts!