I like to use a hole saw for the cutouts.
The tub spouts have test nipples there. After making sure this all holds water, the test nipple gets pulled, the walls will go up and a brass nipple for the tub spout goes in. Leave the galvanized, and you wind up with a bit of rusty water in the mornings. I hate that, so brass it is.
The water is on and looking good.
Right hand drain
Left hand drain.
In the Seattle area, give me a call. I supplied the tubs and the installation for this job.