if the filename already contains the discnumber and the track number you may import them with the function Filename - Tag and a pattern like this:
%discnumber% %track% %title%
the example should give you immediat feedback whether the right data ends up in the right tag.
For resetting the number per folder you may use the numbering assistant (button in the toolbar)::
there you see the options for starting value, whether the total number should be stored and whether the counter is to be reset.
Was this what you were looking for?
Because there is no ability for Mp3tag actions do run in a loop against albums or other groupings you are lost, but you can use a work around.
Write an export script, use the $loop() command to catch all albums, for each album count files and disks and such, create a textual output format, which can be used afterwards by "Textfile to Tag" to import the values into the files.