In personal experience i would advise to use the 240v downlighters as its in the living room. I would use the low voltage downlighters in bathrooms etc...places where steam, water would collect on light fittings.
In the past we have not considered the heat affects of these lights, aslong as there was nothing covering them from the attic / floor side of things (ie loft insulation). If you were concerned, it takes 2-3 mins to check to see if the surrounding plaster board has been affected.. Not that chalk does like..
The advantage for the 240v again the low voltage is that these can be dimmed, where the lv versions would need to have dimmable transformers.
These lights are no different than a normal light, so therefore no permission is required for fitment.
If you were to modify the house, i would inform you landlord, the owner etc for permission, as with downlighters its not a simple case of a little filler and some paint.
I would advice using 5amp junction boxes on the connections, rather than the supplied plastic connector blocks as you are dealing with a 240v connection, not a 12v connection.
Have fun..
Alias