I agree with DG, On the whole when playing a dedicated lab deck with some form of trashing adding a buy or two is a really important thing to do, but in this case I would have probably got a gold asap while also pounding the lab pile; hopefully after the gold buy a hand will be lab-drawn with at least five, and perhaps more, coppers at which time the Mint is a superb buy. I would rarely buy a Mint before the Gold (or Venture, a very decent Mint target).
When to buy the source of buy is a bit of a conundrum; the +buy is very important late game and it is nice to concentrate as much as possible on more important things earlier, but it is painful to draw a huge hand of treasure later and have to waste it. In this specific case I think Worker's Village is certainly the right choice, as the $5 are obviously Lab buys. So maybe any time early to mid-game if a $4 hand presents itself would be a good time.
I personally really like a Lab engine with one terminal and a source of +buy; In the BSW days a lab deck with one Mine and a Market or two was really strong. Now the Lab deck is not really as viable as say an Alchemist or Hunting Party deck but in the right Kingdom, like this one, it can compete.