To slow down the roll drive, move the rubber tyred wheel to the left
so it runs on a smaller diameter section of the large wheel.  If you
cannot move it far enough to slow the music to the desired speed you
will need to fit a smaller pulley to the motor and possibly also change
the belt length.

As for the piano's loudness, the rebuilder may have fitted a stronger
reservoir spring than the original, but I'm sure someone else will be
able to tell you the correct suction value for the Seeburg.  It's so
long since I restored mine that my files are probably inaccessible.

Good luck,

Nicholas Simons, GB