Regarding the crack, I know some people inset a “bow-tie” shaped piece of wood across the crack with the narrowest part of the bow-tie at the crack location. Typically about 1/4″ thick and glued into a recess of the same shape. There’s a name for this that’s not coming to me. Your wood sounds pretty dry and stable, so there may be no need for this.

I agree that filling the knot and crack is a good option. If you don’t, then they will always fill with dirt and snag shirt sleeves, etc. You’ll be able to finish over the epoxy with most finishes. Poly is a great choice for a desk.

Good luck and make sure to post pics of the finished product.