I hardly ever go for Monroe, early or late. Instead I am looking to build up in Northern VA to take Alexandria, and hopefully Harper's Ferry to establish the Potomac Line. From there I am perfectly positioned to press the attack on Washington whenever I see the chance. (Usually shortly after the AI suffers a disastrous loss trying to oust me from Alexandria.)
Monroe is hard to crack: it is deceptively far from Richmond, past your supply lines, well defended with heavily entrenched artillery and can only be approached by water. You are going to need a couple of Divisions worth at least, maybe more, and a lot of artillery. Early in the war that means a large fraction of your fighting power committed to a place where it cannot quickly reach the main battlefields if things in Northern VA turn sour, and you pretty much cede any chance to take Alexandria early by weakening your main Armies (which can barely compete with the large Union stacks around DC as it is).
Not saying it isn't doable, but it is risky IMO, and will take enough doing that you are going to have to sacrifice a lot of doing elsewhere. If the AI has no activity bonus, I might be more inclined to risk it, hoping that she will not be able to take advantage of my weakened main front right away. Against a human I would probably play much more conservatively.
That said, I look longingly at Monroe every game, wishing I could break the Brown Block on Richmond. Take Monroe and your resource troubles are over....