Dave,
I have built my center section before I started the wings, because I was curious if and how these things go together. In the end it turned out fine. There was only one thing. When they drilled the bulkhead parts assembled with the main spar and the splice plates at the factor, they didn't buff the sharp edges of the splice plates, so these knife edges left some marks in the bulkhead parts. I was not so happy with these marks, but I was able to remove them with the Dremel and some of these dentist abrasive rubber tools.
The edges of the splice plate were rounded with the scotch-brite -wheel.
.... the finished center section.
... and one more hint. I read somewhere that the splice plates must be in the fuselage , fixed with some duct tape to the center section, because when the fuselage is built, there is no way to put the splice plates in position.
Peter