Your best option is to call a few plumbers for a quote. it will be difficult for people on here to price it from photos.
Where about in oxfordshire are you?
No, tape should go on the threaded side to be screwed into the diverter, about 10-12 turns of tape. There is no need for ptfe to be used on the compression side of the fitting as its the olive that seals and not the threads.
Are you applying ptfe to the right threads on the fitting? ie the threaded part the screws into the valve. The part where you have put ptfe is pointless and will have no effect, there should be an olive which seals by compression on that part of the fitting.
Inside the waste there should be cutouts in which a special tool can be inserted.
http://www.amazon.co.uk/Monument-325l-Waste-Installation-Tool/dp/B0001P0FSG
You should be able to do it with a pair of long-nose pliers too.
I would either drink a lot more water so your **** doesn't smell so much or bite the bullet and get someone in to look at it, but you may struggle to find someone as we are busy ripping off old ladies, i'm currently writing this from under a sink whilst pretending to fix a tap.
the cartridge is attached to the lever you use to turn it on and adjust the temp.
https://www.youtube.com/watch?v=jToGavSUOgE
I know the tap is different to yours but the principle is the same.
If you are burying them in plaster or concrete the guarantee won't be worth squat as it clearly states not to do so in the MI's.
http://www.johnguest.com/Home/literature-downloads/UK-Literature/DIY-Installation-Manual.aspx
page 6.
Not trying to **** on your bonfire, those fittings will...
Are you fitting an electric shower? if so the plumbing is pretty straight forward and will depend on the model you get. You should choose the shower you want and layout the plumbing accordingly. The connections for the showers can vary between push-fit and compression.
You also need to make...