Well, for a beginner, you're incredibly persistent and patient! :) My personal record for the longest game: 29 months on the "Jedi story" map (but it's a difficult map to complete quickly). A normal time for a typical XL-sized map with a Dungeon is up to 12 months; after that, playing becomes too tedious. So, you should start with simpler maps.
I also had an overflow of money once. However, I reloaded the save before that incident and changed the resources (in such a situation, you can also recruit troops in all cities, even if they are not needed); after that, the overflow did not occur. And yes: the overflow occurs after 2 billion gold, so it's a very rare occurrence.
Regarding assembled artifacts: did you definitely free up all the slots they occupy? Some sets cannot be worn together. If you can't figure it out, post screenshots, and we'll take a look.
Thank you for the advice; I freed up everything, and I was able to put on the artifact. I didn't think that one artifact could take up so many slots.
And there's an interesting point about negative money – you can exchange it on the market for negative resources (however, in this case, you can't buy a hero, build, or upgrade troops, for example).
I solved this problem simply – I gave the negative money to my opponent. :)
