Explanation for increase in the number of oxidation states for transition elements from Sc to Mn of the 4th period
The oxidation state of a transition metal is an accounting device.  It's not the number of "lost electrons".  In potassium permanganate, which has Mn (VII), the manganese atom shares its seven 3d electrons with the ligand (oxygen) in what are essentially covalent bonds, and the "positive charge" associated with the metal is not very different than what it is for ionic calcium compounds.

Regarding "paired electrons are less likely to be involved in bonding than unpaired electrons" -- both paired and unpaired electrons in a transition metal can participate in bonding, provided they are in the outermost shell.  The paired electrons in inner shells are too deep in energy to take part in bonding.