Please note that scanning medium format negatives introduces additional loss of pixels due to different w/h ratio. While 35 mm is 24x36. MF can be e.g. 56x56, which will give you a max. of 4000 pixels square. A 24 Mpixel camera will be like a 16 Mpixel camera under this condition.
As for worms, I’ve seen them when testing with sample images from dpreview.com a few years (?) ago. Preprocessing the scans with e.g. DxO PhotoLab eliminated the worms though.
@gillesp, search the forum for “medium format” to find a wealth of hints. No need to repeat them here!