Yes, I think you're right.
Farms : I'm quite sure I should have done more, so as to get more production. I've almost played to 800 AD and that decision still bites me. (Also, I favoured Forges over Universities in commerce cities, which I now feel was a mistake.)
Build orders : it's a tough call. If you build more troops, you may be able to conquer faster. War takes a bigger toll on your economy, too, but if it ends earlier, chances are you end up better off. Once I know my stack won't get countered, however, the temptation is real to invest in those settlers, far away galleys, set up the National Epic, give the capital its multipliers...
I don't know the right answer, here. Those long term investments also allow to keep up turn by turn with Mansa/Hannibal. It might be a soft spot of mine.
For sure, I misjudged the number of units I needed to capture Maastricht.
Actually, I didn't anticipate I'd go after Maastricht right after Amsterdam's capture. I just happened to see I had 5 units in the area, including 2 catapults. I probably should have adjusted my builds a little more at that point, to get the appropriate melee count, but the decision was made on the fly.