I am in that process now. I did it more or less by the plans on my first wing. second wing the only thing I am doing differently is not riveting the W-1007C rear spar doubler on until after the top skin is riveted access is tight without resting an angled bucking bar on the rivets. The w-1007B wasn't a problem for me.
I don't see where fitting everything first would be an issue, but I didn't want to be juggling both the skins and rear spars on my work tables at the same time.