I have been long arming about 6 years. Most of the time on quilts that have a pantograph in the center and different border pattern, I quilt the top border first. (After the quilt is basted on top and as far down the sides as I can reach.) Then quilt the center. If you will have dense quilting or a dense panto, then you really need to baste the entire quilt before you start. Baste the top, down the sides and across the quilt at the belly bar. Lots of folks are now basting the entire quilt first, then rolling back to the top to begin the quilting.
Then I would do the border (top), do the center entirely, then the bottom border. I don't chunk side borders very well so I turn my quilts. I am trying to learn the chunking on my charity quilts but haven't had enough practice.
And most of my quilts are quilted all over Edge to Edge.
Just take your time and enjoy the process.
Lu in TN