i have learnt in my time as a plumber the best way to install a full sized floor vanity,

*I always use dux 15mmx100mm male brass wingbacks in the wall - for the simple reason that when you have pipes coming down from above the ceiling you can just get a ice-cream container or something similiar and catch all the water in the line between the tee above and the wingback (when the water is off!!!) without any of it spilling down inside the wall (like the female ones do when u undo the plug)

*install the wastepipe (either 32 or 40mm) in the wall with a 88 deg bend facing out (make sure its going to be flush with the wall lining or behind it)
I like to use 40mm pipes instaed of 32mm  for less chance of having a blockage in the future and  I just use a 32 to 40mm trap under the basin

* all you have to basicially do when you come to fit off is measure the hight and width of the two wingbacks coming out of the wall and the wastepipe, and mark it on the back of the vanity, drill 2x20mm holes for the water and one 44-52mm hole for the waste.
 slide the vanity into place, sucure/screww to wall and use white plastic flanges on the three pipes inside the vanity to hide the holes and fit the tap  to the wingbacks and trap and your Done!!!

Linkback: https://www.plumbers.nz/plumbing/1/installing-a-vanity/430/