1) I have a Sky TV box as well, and it communicates via WiFi to my Sky Hub - if I turn the wireless radio off of my Sky Hub then presumably the Sky Box will not be able to communicate via WiFi? (as I doubt it will use the TC... or am I wrong?)
If your Sky TV box only requires a Wi-Fi connection then is shouldn't matter which wireless router you use to connect it to. However, you would have to reconfigure the box to connect to the proper Wi-Fi network.
2) I have a BT Duel Band WiFi Extender 600 on my top floor, will I be able to connect this to the TC (or is this something I'd have to consult there literature on)
Most likely, the BT extender will NOT work with the TC if the connection between them will be wireless. This is typically because each manufacturer use their own propriety methods to extend their own network's wireless networks.
What is will come down to is exactly what is(are) your networking goal(s) for the TC and then understand the limitations that are imposed by implementing a mixed-vendor network.
3) Should I connect my other ethernet's (i.e. iMac and Home Plug) directly to the TC... or does it not matter if I'm only disabling the wireless radio of the Sky Hub?
It shouldn't matter. I am assuming that the Sky Hub uses 1 Gbps Ethernet ports as the TC does.
I presume the answers above will lead me to moving the TC to my living room... if I follow the guide from your previous message does this mean that I would have one network and that devices would switch between both my TC and Sky Hub as required without me having to manually select which network they should use?
That is correct.
Not sure if I'm making sense, but ultimately would my Sky TV box still communicate with my Sky Hub, but my iPhone use either the Sky Hub or the TC depending on what device gives the best signal?
Unfortunately, I am not familiar with the inner workings of the relationship between these two Sky products. If the TV box requires connectivity to the Sky Hub (and not to just any other wireless router), it should continue to work with this roaming style network by connecting to the Hub ... but that will depend on where it is located with respect to that Hub. Make sense?