On garden rushes:
Three piles are 26+-2 cards (Gardens, Estates, ...).
Without gainers, you probably can't get more than 2 cards at turn, or (maybe with Woodcutter or Pawn) at least not more than two cards that aren't Coppers. Especially something like Gardens+non-Copper is pretty unlikely.
During your opening two turns, you won't get more than 2 cards for the piles.
So you have to get 26 cards from turn 3 on, let's say 8 Gardens+8 Coppers on 8 turns and 10, say, Woodcutter or Pawns+8 Estates on 9 turns, which also means you have to get 17 turns with at least 4$ in a row which won't happen.
Even if it happens, you'll end the game in this case on turn 19 with 38 cards in deck, 8 Gardens and 11 Estates. Let's say you hit 40+ cards thanks to Pawn (though I don't know where the money comes from if you use Pawn for +Action+Buy, or Hamlet instead, or or or).
This means you have 43 points in ~20 turns with more than optimal, close to impossible draws. An opponent with 6 Provinces and 2 Duchies still wins here, and this should be more than possible in 20 turns.
So I don't think a Gardens "rush" in the case (+buy action as support only, no engine) you had could work. You probably should buy more Silvers early on, but than it's even less a rush, and you can only win if your opponent can't pile all the Provinces himself or, while still leading, end the games on piles.