The guide basically assumes you use Patient Sniper since it's so much better. Most things will work for non-PS players, but the opener will definitely be different if you're not using Patient Sniper. Can't imagine why you wouldn't, but whatever.
1: You don't have to cast it immediately because you don't lose a cast by delaying it. As long as you get it off within Vulnerable, you have maximized the # of Marked Shots you can do in a fight, and the damage they do (providing you use Sidewinders probably, which is inherently tied to Marked Shot).