please, see me answers below.
1) once we setup on-premise local OC site, APIs and services are synced from your central and all data that we are providing by OC provider and experimenting with by OC experimenters are saved on-premise on local OC site?
When you setup a new OC site, the only synchronization is between the data in your local OC site and the "central Orion". This means that data created/updated in you OC site, appear updated in the central Orion. Note that it does NOT happen the other way around: data in the central Orion is not updated in your local OC site. APIs, services etc. will rely on the "central Orion", so you don't need to replicate these services.
2) when you update some API on central it's synced automatically to OC site?
As mentioned before, the synchronization only takes place from the local OC site to the central one, but not the other way around.
3) What about accounts, are they also residing on OC site or OC tier, once they're registered?
Again, all services are at Organicity level, not at site level. When you set up a new site, you only federate data; services are not replicated.
If take a look to the figure here , you can see that OC sites are connected to the Organicity Platform (through Federation API) and services use the data in the platform (central Orion) through the EaaS API. So a new OC site just uses the federated API to inject data, and that is all.
Luis / Organicity Team