Wouldn't worry about it, it has a noggin below and is screwed into the 3" stud. Drill from the 1.5 side though so you're bang in the centre of that. Drill down on the angle so you can bend to your mixer pipework easier. As I said, I'd make up copper L pieces with solder elbows and clip them to...
If you're coming from below come back up the left and just drill through the stud above the lower noggin. Just make sure not to hit it with your hardie screws later.
If you're not worried about supporting the mixer bar then definitely taking the cold onto the right hand cavity is the way to go, then at least you're central to the bath taps and the riser is supported. It doesn't need to be difficult, just make a hole through the vertical stud near the ceiling...
The pipe centres are 6" apart, you don't need to chop any out. You need to get your cold feed on the right hand side of the central stud though. I'd also add noggins (the crossmembers in your picture) on either side of the stud where you want the mixer valve and use your template to mark pipe...
I wouldn't recommend amazon for electrical items, better getting something from a UK supplier. One of the requirements of selv is to isolate the mains earth from the outgoing supply, it would be easy to see a scenario where a cable comes loose and touches the metal casing of that unit. I very...
Yep, youll probably even have space to secure it to the underside of the joist with a clip to keep it tight and out of the way, or all round band if youre putting oval in your chase.
That sounds crap. Honestly watch this video. Fit your isolators to the drops and you can then connect your pushfit pipework further down. You'll need a length of copper pipe and a bender if you don't want to solder.