Best check with a sparkie - but at the very minumum I would do your bath and sinks, also cross bond all your heating pipes, gas, oil pipes and make sure you have at least one return to the main earth on your consumer unit - but I am not an electrician
I would ditch the damproof lining - you shouldn't need it. Apart from that leave a small gap at the top to allow the walls to breathe, also if you do the roof allow a small gap to allow condenstation to run out
The only snag with 'water proofing' wood is that it can't breathe - just get a good quality varnish, or paint and accept some water wil get into the wood - if the room is warm and it is not a wetroom then I wouldn't worry about it too much
No, but the sealant would bind to the loose grout and could work free over time - why don't you dig the grout out, you can buy grout removers to fit into electric drills - Screwfix do them - and then regrout with a flexible grout for your type of floor
Don't take your rad stats off as they can still be used to control the temp of all your rooms individually - all you need to do is make sure you have a 'minimum flow rad', by that a rad that is always on to give your bolier something to work on - you can get spring loaded adjustable valves that...
My drains have blocked up twice in th elast 2 weeks - I need to push 2 sets of drain rods down to clear the blockage - if they block again can i screw a 3rd set of rods on and push whatever seems to be blocking them all the way to the main sewer - does my drain just drop straight in or is there...