Ryan:
Everyone does it differently, but here are my own personal answers:
a) I think you have to go back and forth between the property and the map. I prefer to get the map first for an overall sense of things and to find a few potential holes to check out; otherwise that first visit is a lot of wandering around trying to get a sense of scale of the place.
b) I know Bill Coore didn't use a topo map to route Sand Hills ... they only had a 5-foot contour map and he said it left out too much. But, Sand Hills is treeless so you can see all the contours. In trees I would think anyone would need a map.
c) The natural features which are most likely to influence the routing are vegetation and views. Sometimes there is a cool contour that you miss on the topo (usually because it's a subtle thing that is hidden between the two-foot contours on flattish ground), but you may miss those until you get to construction. It's hard to adjust one hole, there is usually a bit of domino effect.
d) Insistence on returning nines reduces the options more than any other decision. (Last night, I had three of my associates guess how many times we had not returned the ninth hole to the clubhouse -- it was 10 out of 25 courses.) A par-72 mandate limits options more if they are insistent on a 36/36 balance.