Hey, I've done that once (or twice) myself.
The CSA has about a hundred variations of two basic strategies. Take Washington D.C. as soon as possible and crush the Union NM or take advantage of the defense by fighting them to a standstill for Victory Points.
To blitz D.C., make an Army under Beauregard with all the 20 lbers you start with, Divisions of your best troops led by Jackson, Longstreet and Shelby etc. with Huger along to boost the artillery effectiveness. Put a Marine unit in each Division so you can cross the Potomac quickly. I took the Union Capital from a maxed out Athena in Oct. 1861. The statisticians figure this only works about 40% of the time, but the threat works 100% of the time. If the Union player wants to concentrate on the Mississippi or take New Orleans or just set back and build the largest blockade fleet, then take D.C. Veteran human players know this is coming and keep D.C. covered. If they don't...
So plan B would be to dig in your heels and fight it out. I prefer to have a thin line of one Division with a supply unit (SU) per region entrenched inside a stockade or redoubt backed up by Lee with an Army in VA. A stockade adds a big bonus to your lone Division's Zone of Control so that a Union Army entering the region is stopped dead. The defensive position is a hard nut to crack if they assault without preparation. With the SU, the Division only has a 5% chance to surrender. If the blue bellies lay siege, then Lee can go around them to cut off their resupply/retreat path (it's called a line of communications). You have enough Region Decision Cards to build a redoubt in Manassas in '62 along with stockades to your left and right (Clarke and Stafford VA). Lee can react to any of these from Culpepper. If the Union tries to go down the Shenandoah Valley, then the door to D.C. should be open a crack or two. They can't be strong everywhere and any attack will be half stepping if they have to cover their Capital.
You can also put 3 stockades in the so called West between Fort Pillow and the Fort in Dover TN (Dyer, Gibson and Henry, TN). An Army under Johnston can be your reaction force there. This should take a strong Union force to beat and they will be missed in the East.
P.S. After First Bull Run, Jeff Davis ordered the Army to march on Washington, but the troops were too spread out chasing fleeing Yankees. By the time the Army reformed, the opportunity was lost. So blitzing D.C. is not ahistorical.
I'm the 51st shade of gray. Eat, pray, Charge!