3p: Alchemist
3: Watchtower
4: Ironworks
4: Treasure Map
4: Spy
5: Council Room
5: Saboteur
5: Bazaar
5: Market
5: Venture
Random thoughts on potentially intersting cards and the setup:
a) Ironworks -> no intersting cards for <=4.
b) no trashing
c) Only expensive cards for action/draw Engine
d) Treasure Map is difficult under this conditions
e) Venture also
So for me the interesting cards is the Alchemist in this setup. Spice this up with a Councilroom in midgame for +Buy. So start would be Potion/Silver. Get a second Potion somewhen to stabilize the Alchemist chain and get more, 1 CR, +some Gold, see what happens. 5/2 take the Councilroom to accelerate the start, Market, Bazaar, Venture are quite weak at the start, Saboteur is Saboteur, but of course a danger for the alchemists if you don't manage to get them back on top of the discard-pile (or if you have more than 5, which is prob. not a good idea against saboteurs anyway).
Alternative take Markets instead of CR, but I would guess CR is stronger.
Seems like a good question for Geronimoo's simulator...