Walter R. wrote:
What would be the advantage of a layer of sand? How thick a layer do you
have in mind?

Neither concrete slabs nor brick are perfectly flat. The high points
will concentrate stress and possibly crack the brick. Pavers are
stronger, so it'd be less of an issue, but the sand will make getting a
flat level surface to walk on easier. A 1/2" sand setting bed is fine.
Cheap insurance.

If I lay the brick directly on the concrete, albeit with hairline cracks,
would that not be more stable and less apt to generate weeds?

No. Those little hairline cracks are enough to let material enter.
Material that will consist of plant matter (read foor) and seeds (read
food eaters). You might not get growth right away, but when you do
it'll be tougher to get rid of the weeds.

If you're really concerned about stopping the weeds, they make
fortified sand mixes for filling the cracks between pavers. It's
brushed in, sets by sprinkling with water - best thing to prevent weeds
from getting started.

R