Count of Selected Tracks

For formatting tracks, it would be nice to be to have a field that contains the number of tracks selected, like you can see at the bottom right of the screen.

I want to be able to use this for formatting the track xx/yy.

Is this possibe?

check out the track numbering assistant.
(Ctrl K) There you can set which numbers should be stored in the field TRACK and/or discnumber.