(2) Why didn't you get a Remake on T1? Even for BM, clearing those first Estates and turning them into Silver can be huge.
I agree because it's a Colony game, but I've always thought Remake is awful (because it's too slow) for BM in Province games. Am I wrong?
As for the actual game: definitely get the Remake on T1.
At the end of T17 you draw:
mail-mi: turn 17
...
mail-mi draws Copper, Remake, Silver, Colony, Gold
Your T18:
mail-mi: turn 18
mail-mi plays Remake
mail-mi trashes Silver
mail-mi gains Potion
mail-mi trashes Copper
mail-mi draws Copper, Copper, Gold, Silver, Gold
You really don't want the Potion here. Just don't play the Remake and buy a Gold.
On T20 and T21 you buy a 4th and a 5th Platinum with 3 Colonies gone already. These should just be Provinces, especially the T21 one because your Margrave play triggered a reshuffle.