What kind of wall is it? When was the house built? You don't really want your hot water pipe running in a wall like that, can't you strip the plaster back and box the pipes in?
The waste will be 32mm for the sink. I'd be chasing it in all day long. If it's getting dot and dabbed there will be a 10mm ish gap between wall and board also. Pipes effectively need chasing In a very minimal amount. You can't run them external on show and why bother with a boxing in?
I used to hate fitting those wall hung basin,s customers never thought where the pipes would go stud walls are ok coz you can just cut a section out and replace afterwards, best bet is build a stud wall if its possible.
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