the only requirements to set up and OC site are the ones commented in the tech. docs. In a nutshell, when you set up and OC site, you federate your data with Organicity, so that the data of your site are also in the "central Orion".
Besides, the "apps" and experiments are at Organicity level, so there would not be something like "OC site apps", but "apps" might use data that you have federated.
When an OC site is set up, new data created or updated is also updated in the "central Orion". So in case of Internet access failure, there is not much to be done (i.e. some updated will not happen).
All in all, when you create a new OC site, you do NOT replicate the whole Organicity infrastructure, but you just federate your data. In this sense, the only requirement is a server with some storage to run what is detailed here .
Please, let us know if we can clarify it further.
Luis / Organicity Team