At some point you’ll need to make it a component or a group but if you want the sink to cut an opening, it’ll need to be applied to the face. If you make the counter a component first and open it for editing before adding the sink or you make a component of the counter and the sink makes no difference.
That sink does not have a hole-cutting attribute but that could be added. That hole will only cut through a single face so you would probably delete the bottom face of the countertop. That’s not going to be a big deal since it wouldn’t be visible. Alternatively you could draw an opening in the countertop and make a real hole in. Draw the shape of the open much like you would if you were preparing to cut the real countertop. Then use Push/Pull to push the waste away.