My attempt:
2: Moat, Faithful Hound, Guardian, Courtyard
3: Tunnel
4: Diplomat
5: Band of Misfits, Royal Seal
6: Hunting Grounds
<8>: Overlord
Landscapes: Sewers, Tomb
Moat, Faithful Hound, Diplomat, Band of Misfits and Overlord all have the same effect (+2 cards), and they are all outclassed by Courtyard. Guardian is present if you want a delayed Copper instead of a Courtyard, but there are no attacks for it to prevent. Hunting Grounds and Tunnel are present but can't be activated. Royal Seal isn't especially useless but I think it has the least impact of the remaining cards.
I don't think any strategy beats BM-Courtyard, buying Royal Seals instead of Silver when you hit $5 (maybe Hunting Grounds?).