Not only do you need to manually define the attributes (variables) that will hold the custom stats values,
you would also need to redefine all of the scripts that need to use those values.
For example, I assume MATK, MEVA, STAM will be used in battle, so the battle scripts would need to be
modified to use them.
FAITH, on the other hand, would probably be used exclusively in game play, so you could store & modify the
value in a game variable, and check the value of the variable, using event commands.
(you may only need to have the STATUS menu modified to include the custom stat.)
Be Well