For gold on the last and longest level of the game, my strategy has always worked:
What to buy as soon as you can afford it, selling bears along the way to help with finances:
1 duck - buy first, then send the truck with second bear
... don't buy water until absolutely necessary, when the grass is gone
... don't sell any eggs or egg solids, only bears
1 egg solids plant
... at 2:30 min, you get 4 bears - trap two. Warehouse one, send truck with it, warehouse the other. Then try to slow the others down with only two clicks (for fully upgraded cage) until the truck comes back. If the duck gets too close, you'll have to trap them and forfeit that bear sale, but sometimes you get lucky and can sell at least three. If you sell only two, send 6 egg solids with the second bear.
1 bakery
1 more duck
... upgrade warehouse - either around 2:30 min or after the 2nd duck
upgrade egg solids plant & bakery
1 more duck (total 3)
1 sheep
1 spinnery
1 weaving mill
1 more sheep
upgrade spinnery & weaving mill
1 more sheep
2 more ducks for necessary 5 - upgrade warehouse but not duck buildings
1 cow
sell ducks, keep processing stockpile of eggs
1 churn
1 cheese dairy
2 more sheep for necessary 5
1 more cow
upgrade churn & cheese dairy
sell sheep, keep processing stockpile of wool
1 more cow
upgrade churn & cheese dairy
repeat last two lines until you get your 40 necessary cheese
I just played the level again, and even losing my first cow immediately to a bear, I still finished the round in 34:21 min, well under the Gold level limit.