3 the 2nd level in the city can be automatically completed with the feed act. a cat who is unlocked during the house with this act is bred. the wholesome cats wiki has all the acts needed to automatrically complete stages, but some stages don't have automatically completing acts.
and a good way to earn coins quick is to swtitch to the mobile phone app and log in and play there, since the mobile app has the coin shop option to trade 1000 fishbones for 1 coin. other methods include finishing boss fight stages and selling cats. (1 starred cats can only be set free, though!) here's the chart on the wiki:
1 starred cats can only be set free
2 starred cats can be sold for 1 coin
3 starred cats can be sold for 1-2 coins
4 starred cats can be sold for 2-4 coins
hope this helped! side note; feed is also useful for future city levels, and the 2nd level of fields.