RE: If you were my Mauser, what kind would you be?
 

I would take the gun to any well respected gunsmith for an opinion on whether the action appears to be of decent manufacture. Visually it appears fine to me, but really hard for me to say with a few interent pics.
And the loads you could use would be straight out of the loading books. You'll customize it for your own gun but I would juststart a little below the medium velocities and work up slow to just below the maximums, assuming you see no pressure signs on the brass, sticky bolt, etc.
140 grain bullets will probably do well, but I have an old 7 x 57 that loves 160 grain Sierra's.