Nektarios
I would suggest you contact one or more of ROCOR's bishops directly to get something more authoritative, but here's how I understand things:
Who is ROCOR in communion with, Offically?
I'm not sure that anything can be said to be "official" and definite with regards to who ROCOR is in communion with. Certainly, ROCOR would say that they are in communion with: the Serbian Patriarchate, the Jerusalem Patriarchate, the TOC of Met. Cyprian, Greek Old Calendarists in Bulgaria, and Greek Old Calendarists in Romania. In practice, there are indeed concelebrations and communion between ROCOR and these groups. There seems to be some hesitancy to make things totally cut and dry, though.
2. Are they SUPPOSED To communion outside of ROCOR, except to the Cyprianites?
It is my understanding that those who are part of ROCOR could commune at parishes in the groups mentioned above (provided the priest knew the situation, they were prepared, etc). As to other groups (OCA, GOA, etc.), I think this would be something you would have to talk with individual priests/bishops about, and would depend on many factors.
3. What do they think about the GOC of Greece Synods?
There is a wide variety of opinion. Some think that ROCOR did a terrible thing in ever having relations with the Greek Old Calendarists. Some think that we should reestablish communion with the "strictest" of them immediately. And there are all sorts of views in between. Generally, ROCOR is more friendly towards those Greek Old Calendarist groups who do not condemn the new calendarists and ecumenists , and are not quite as friendly with those groups who are "less moderate".