Pairing only matters when they are not closely matched and if yours are evenly warm, this is OK. If for some reason you are in doubt of burning your finger or not close, use three.

Using 2 1N400x's works for this use. For mass production, others would be better.

Pairing only matters when they are not closely matched and if yours are evenly warm, this is OK. If for some reason you are in doubt of burning your finger or not close, use three.

Using 2 1N400x's works for this use if as you say is OK if convenient.

For mass production, others would be better.

How did you verify Imax ? power supply spec or measured?