To mark the centerline, set a compass to span something more than half the width of the leg. Draw an arc from corner of the leg. The point where the arcs intersect will be on the centerline. With a centerline point on each end of the leg, place a scribe on the point, slide a straightedge up to touch the scribe. Do the same on the other end. When you have the straightedge positioned so that you can touch both points with the scribe, and in each case it is touching the straightedge - without moving the straightedge - scribe the line. Use scribes, rather than pencils or pens, because they make more precise marks.
In the "Getting Started with Woodworking" video, the holes through the 4x4's were drilled from the back. That is, they start on the side opposite the precisely-positioned mark, and drill through to hit it. If they can do this, more power to them, but I can't drill through 3-1/2" of wood to emerge at a precise mark without a drill press - and not always then.
Finding a toolbox for a mechanic, for his hand tools, is not a big challenge at all - there are dozens of the tool boxes available on the market, from huge roll-around shop cases to small metal boxes. Plumbers, electricians, and farmers are well served, too, with everything from pickup-truck storage to toolboxes and belts. But, if you are a shop-bound woodworker then the case changes. You get to need a tool box that suits the range and variety of hand tools that most woodworkers like to have. For those who deny making do with second best, there's only one solution, you’ve to build a wooden toolbox that should be designed expressly for a woodworking shop.
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.