Is there a proper or recommended length that a bathroom faucet spout should extend over the sink? A lot of them extend 2" past the edge which seems too close.
That is a function of the faucet's design, the location of the faucet holes relative to the basin, AND the shape of the basin. Usually you do not have many options once you pick the sink and faucet you like. If the holes are not on the sink itself, the location of the holes in the countertop will be governed by where they can be made without interferring with other items and still allow the faucet to be secured and installed.