Here are some answers for you
1.) I assume I will need to pay for the big switchboard thing and terminals in each room (2 bed flat - would probably want 2 connectors in lounge, 1 in each bed and perhaps one in the bathroom). How much is this likely to cost?
That depends on how much the developer is putting in as part of the package and you may well be forced to use the orginal installer to finish the job which was part of the developers deal. Out of interest who is the developer?
2.) Are you able to do in wall connections as well - for Plasma wall mounting and speaker positioning around the room?
Lexcom plates are bloody ugly, however we have the little RJ45 plates engineered to fit other faceplate manufacturers. You then use little adaptors to conver the signals back to TV, Telephone and autio connections.
3.) Am I limited to installing the Lexcom system as there do appear to be a few limitations:
i.) Composite video connection that is offered is lower quality than I usually use (component or above)
ii.) I have SKY HD and would ideally like to split the HDMI signal and route that to 3 different HDTVs (lounge and 2 bedrooms) - is this possible with Lexcom or with anything that is compatible with Lexcom
iii.) Lexcom site says it can't support Dolby Digital 5.1, only stereo - is this true as it is not really good enough for watching SKY HD, films from PC /DVD or console gaming (Xbox 360).
Technically you are not limited to installing Lexcom kit on the end of the lexcom cable, however this may end up restricting you even further. ie not having any coax tv points in the apartment. In its current guise the system can only pass UHF and Composite signals. Depending on howmany cables are pulled to each location we can use two cat5e/cat7 to get full HD Component and audio to a location.
4.) Is this an upgradeable system? - what does it actually offer? (the marketing material is generally very unclear!)
It offers the choice of tv (UHF), telephone, data and audio over a single cable type to generic locations throughout the appartment. You have complete choise over what signal appears where by patching the different services in the central cabinet out to the points in the property.
Hope that helps.