Our daughter Gloria has been really fussy lately. It starts with a whine, but escalates quickly to a full body tantrum, her arms flailing and back arching, and her voice rising to a scream. It happens so fast that I almost drop her, as her torso morphs from cuddly curl to hard column and her heels accelerate towards my crotch.
I have the same conflict about being reactive. In addition to your point about kids learning from what you do, I believe that a plan for how you're going to raise your kids, at least one on a day-by-day basis, can't be successful, because we don't know ahead of time what our kids will need from us. We can plan ahead that we want to teach them integrity, kindness, patience. But they will come to us one day with anger because they're being teased, and a different day with a conflict over whether to admit a mistake, and another day with difficulty focusing on their homework. I think being proactive is knowing your values, but the work is often finding the right way to apply them to the challenges our kids are facing at any given moment.