firstly if the box of cat5 is more than 7-8yrs old then its most likely cat5 not cat5e, I strongly recommend you dont install cat5 but cat5e. GPO = General Power Outlet, ie power socket.
A single cat5e/6 run can be used for Fastethernet plus phone or GigE and no other service, ie there are 4 pairs, two for fast ethernet or 4 for GigE, if only use fastethernet then the one other can be used for phone. I strongly recommend that you simply wire all sockets as full 4pair (8wire) and use external splitters should you decide to run phone and data, that way you can revert it to GigE at a moments notice and no tools.
I cannot feel that you have overcooked it slightly, I am still not a strong believer in the need for HDMI to everywhere, its a major waste for minor bedrooms etc, my preference is to simply distribute FreeView UHF to TVs and a UHF modulated run of whats on the Sky box. I know many reel at the thought of distributing the Sky via UHF but I have provided both UHF and HDMI solutions to clients in the past and at first install they just go with the UHF and say come back once we have settled in and sort the HDMI solution, after a few months they typically ring back and say dont bother as the pic on their 26" bdroom TVs is just fine. dont forget the FreeView is still in HD for TV1,2,3 etc.
Therefore in a your minor bedrooms I would go,
1x cat5e, 1x RG6 and GPO behind wall mounted TV, the cat5e is to feed the builtin media client, the RG6 to supply UHF FreeView and a analog UHF feed from Sky box.
Below TV I would consider 1x RG6 for optional extra Sky Box and a single cat5e for data and/or phone, also provide an HDMI to the TV above. Also run a single cat5e beside the bed for data and/or phone, to have more data in a bedroom (unless its a study also) is a waste in my view, ymmv.
This general layout can be used in most non major AV locations, but in the location of the major AV where the prime sky box goes I recommend 3x RG6 plus 2 or 3 cat5e (down low), 1xRG6 and 1xcat5 to the TV on the wall above, at least 2xHDMI between the two, I think this is a bit more efficient than you design. Obviously I have not included any HDMI.
I suggest you read the HDBaseT standard I linked, this will take over from HDMI distribution and uses a single cat5e to distribute all that a HDMI carries plus FastEthernet and remote control, so that cat5e behind the TV is important.