So I've just played the last mission till the end and spared the boss. I've digged free the whole dungeon and did all the research so there's plenty storage for gold and mana. No enemies entering the dungeon, several endless gold veins (at least 7, the ones with ruby and emerald in them) and 16 naga collecting mana. A good storage of beer might also give you the beer achievement.

If you don't feel like grinding the achievements through normal playing just let the game run with that savegame.

By the time you have the gold achievement, make sure to switch the workers for more nagas because you will only need them for making some beer now and then.

(Let the game run in windowed mode, so your minions keep collecting while you can do other stuff.)

https://drive.google.com/open?id=1jFIN2Nbh44__KNRzFTCJ4DYcQqhyHV-_

Let me know if it worked out for you!