I overbid the solution to 1) to 781, though I think even more should be possible. The card that is played this often is Procession.
The main idea is to create (almost) infinite procession chains. This works in the following fashion using Processions or Band of Misfits (P) and Graverobbers or Rogues (with Watchtower) (G)
assume we have n P left, 2 of which are in the trash, also 1 G are in the trash then
play P1
... play P2
... ... play P3
...
... ... ... play P(n-3)
... ... ... ... play P(n-2)
... ... ... ... ... play G(n-1) get P(n),G(n) on deck
... ... ... ... ... trash G(n-1)
... ... ... ... ... play G(n-2) get P(n-1),G(n-1) on deck
... ... ... ... ... trash G(n-2)
... ... ... ... trash P(n-2)
... ... ... ... play G(n-3) get P(n-2),G(n-2) on deck
... ... ... trash P(n-3)
... ... ... play G(n-4) get P(n-3),G(n-3) on deck
...
... ... trash P3
... ... play Card Drawer (drawing all cards put on deck)
... trash P2
result P1 stays in play area P2,P3,G3 are in trash so that n' = n-1
So we end up with 19+2*(16+15+...+1)=259 plays of procession. If we cleverly start all of these chains on a KC, we get another factor of 3. Furthermore, the two P are not in the trash in the first of these loops, so that we can add another 4 plays for a lower bound of 781 plays.
Ways to increase this number:
a) After all BoM are gone, we may gain the last procession and add it to the pool ~60 plays
b) There may be some clever trick to gain/trash Cultists to draw some of the processions so that some can be played twice. I estimate at least 200 plays.