I was going to do it in sections
and leave the screed boards buried in the sand and not remove them.

Where do you live? Do you have freezing weather?

We built a 1100 sq ft brick patio this summer, and also did it in
sections. When we finished one section, we'd remove the screed pipes,
fill the groove with sand, tamp it, and move to the next section.
Worked great.

If you get freezes, wouldn't the frost heave push the boards back up?