For our undermount SS prep sink, the countertop people took the sink with them to measure for the cutout and then they attached it when the countertop was installed. Of course the plumber needs to do all the hookups. For my farmhouse apron sink, the kitchen designer built the cabinet to the correct measurements, then my carpenter built a support on top of the cabinet and had it in place for countertop template and install.

Your very questions are why I chose to bite the bullet and use a GC. We're doing some things ourselves, but letting the GC coordinate it all, including the custom cabinet guy, who insists on doing his own finishing and install, which I'm happy about.
I can only tell you what we're doing, in this order so far. (small kitchen redo)
--Strip wallpaper and remove chair rail and paneling
--Remove existing appliances
--remove cabinets
--drywall demo to re-do electrical in certain areas
--electrical - removing old, and adding new stuff (hardwiring, new outets, switches etc)
--drywall repairs
--electrical finishing
--prep walls for painting, apply tinted primer and two coats
--fill in floor tile where cabinets will go in.
--install cabinets
--finish electrical for under cabinet lighting.
--install new light fixtures
--install new appliances.
--countertops - if we go with quartz, the countertop people will install the undermount sink - GC will install a brace for extra support.
--plumber to run new water line for fridge, and install DW, GD, hook up sink and faucets.
--electrician to install new appliances if we needed this but we will have a freestanding range so it's not needed.
---final paint touch ups.

So, as you can see, most workers have to come in and out at different times to do rough in and then finishing work. That's where it gets hairy coordinating those things.