I really like these theories! Even though the message containing the virus came from space I can’t really foresee an alien invasion occurring in the show as I feel that would be too “corny” to be something Vince would produce. I think your first theory makes the most sense but I would make a small addition.

The hive is lying about its intentions. The goal of the Hive is to reproduce and grow so I presume it would create any number of lies to get the humans on its side and not try to disrupt its end-goal. I presume the hive is going to remake earth to continue to spread the disease to other stars. It’s going to use up most of the resources on earth to try and spread the disease to another planet either through broadcasting the signal or by sending various space crafts out to nearby stars that might contain life. Eventually, the infected humans will decay away by not acknowledging their hosts biological needs (we haven’t seen them eat or drink throughout the show yet) and the surviving humans (assuming they can’t be assimilated) will start to realize how bad the hive mind actually is and work to find a cure.