New classes as mules?

i want a demon slayer main
if i level two demon slayers to 70
can i stack the link skill from the second one to the first one?

and if they do stack


12 slots per account right?
what would be better
cyg@120 = 24att/30att post patch
10 cannon shooters for +150 all stats and +50% hp
10 demon slayers for +100% boss
10 mercedes for 2x exp (lol)

all linked to a main

because if you can link more than once
this has potential for being completely broken haha