I drilled from the mark. That way I could ensure that the hole was where it was supposed to be, on the side where the position was critical. I have two 3/8" bits -- a brad point bit that came with my doweling set, and a perfectly ordinary 3/8" twist bit. Brad-point bits are far more precise than twist bits -- they're more likely to start where you want them to, and they're more likely to stay straight. My problem is that my brad-point bit wasn't long enough to go through 3-1/2" of wood. So I started each hole with the brad-point bit, then finished it off with the twist bit. I clamped a piece of ply on the back, to reduce tear-out.
My advice? Don't do this. If you have jointer and a planer, use them. If you don't, seriously consider using dimensional lumber that has already been planed and sanded. If you are going to try to clean up construction lumber by hand, using a hand plane is a lot faster and more pleasant than using a belt sander. Except, of course, that to do a good job of planing a board you need a solid bench to hold the board, and you don't have a bench, yet.
While a strict figure for the bench’s weight capacity is not available, a quick browse through their other stand and bench products shows a general weight capacity well above most other brands. As such, while we cannot say for certain that this bench provides the best weight capacity, it is more than likely that it the capacity is similar to the other products in the catalog.