After clearing the first league, I'm finding it difficult to accumulate enough gold to upgrade my hideout. Upgrades are costing 25-30k gold and it takes many hours to passively generate that gold. I find that any gold I do store gets stolen quickly, resulting in me getting nowhere. What are some effective strategies for collecting and holding gold?
If you are being stolen quickly, it means your dungeon is easy.
Look on YouTube some layouts to help you get started with good defenses, and after a while you will know what is possible to do with each trap given each dungeon.
The traps you find on internet are pretty good for low levels where most people aren't hardcore gamers and don't do the same, but after a certain level, you will have to come with innovative layouts because all the ones you find on internet are well known.
Besides the layout improvement, upgrade your traps so you don't get your gems stolen so easily and a very importart upgrade: Skull bonus.
If you get that upgrade up to 400 gold for each skull, you will make money for the initial upgrade really quick. You will be gathering 80k money pretty often.
Though you probably have already figured this out all by yourself during this whole year it took someone to answer this question.