There is a non sequitur here. "Leo" represents a direction in the sky, in which we are moving "relative to the CBR". "Leo" does not represent an object wrt which we have a relative velocity.
Not knowing any better, I would have to suppose that our velocity wrt the brighter stars of the constellation Leo, are significantly less than the cited 390 kps.
I await instruction to the contrary.
Is the north end of the earth the front of the spaceship? Or are we traveling “sideways”?
I think you are right. The author says that our total velocity is in that direction wrt CBR. What he did not say was that Leo is rotating around the center of the Milky Way with us so our composite velocity is slowly changing angle as we spin around the center of the galaxy. It is just for our lifetimes velocity is in the direction of Leo.