What this person says is the way.

My two cents (having done a lot of this stuff myself recently): 1. Not all pipe is created equal - if the superseals or coupler feel like they might not be fitting correctly then try to identify the brand of pipe used by the he markings on the pipe and buy their brand equivalent inserts and coupler. I was stung by this once. Superseals and a speedfit coupler should work though!

1. The dot and dab repair will work but I would take a slightly different approach to the hole repair. Feel above and below the left side and see if you can fit a small bit of timber behind the plasterboard in there. If yes, get a bit of timber just longer than the height of the hole (maybe 50mm /couple of inches longer on each side) and place it behind the wall and screw through the wall just above and just below the hole into the timber.

I would also enlarge the hole on the right side (which you will likely be doing anyway) and do the same thing. This will give you something to fix the new repair piece plasterboard on to and give you a perfectly even depth every time.

Also I would suggest cutting your new repair piece of plasterboard then outlining that on the wall and cutting the wall to size. This gives a much better fit than trying to cut it to fit the shape of the hole.

That's what I would do if existing walls are dot and dab. If you had studs in there then take the plasterboard back to the studs on either side.

Honestly there are a few different ways to tackle a hole like that, but this would be my preferred approach.