You really need to test this yourself. If there is more than 300dpi of data in the print (will depend on the paper, the enlarging lens and how well it was focused) you can capture it with most good scanners. Just make scans at higher resolutions and look at fine detail. Resize them all both up and down to the same pixel dimensions and see which give you the best scans for the purpose of the output.
Yes, scan to 16bit tiff if you will be doing major adjustments to them. Just to post online jpeg should be OK.