The CHURCH, right, but before that, the Christians were already there, in secret. The early communities were a jewish sect, each community (which means each town) had his own bishop that was selected from the members, men and women!
The catacombs were tombs, so no one went there as long as it wasn't a funeral, guess why they met there... because no one was following them there. The early Christians hid in the catacombs!
Wrong. The fish was (still is) the sign of the Christians because the ancient-greek word for fish is ICHTHYS which can be used as an acronym for
IΗΣΟΎΣ Iēsous „Jesus“
ΧΡΙΣΤΌΣ Christós „Christ“
ΘΕΟΎ Theoú „Gods“
ΥΙΌΣ Hyiós „Son“
ΣΩΤΉΡ Sōtér „Savior"
This is right and has nothing to do with the Catholics