Scanning strategies

Is there a "rule of thumb" in the following three cases in order to
achieve best results:

1. Scan to desired resolution or use maximum optical resolution, do
all the processing and only then, as the last step, reduce resolution?

2. I read once that above strategy should be used for tonal range for
optimum results e.g. scan at 48-bit depth for maximum tonal range, do
the adjustments and then reduce to 24-bit.

3. This is really a subset of the above and relates to grayscale.
Again, I read that it pays to scan B&W in color for the same reason -
wider tonal range - and then, after processing, reduce to grayscale.

Any comments? TIA.

Don.