Also make sure to expand your side shop whenever you get the chance. Once I fully expanded my shop....I think you can sell up to 12 items.....the money started rolling in. You just have to keep inventory full to be at the top of your neighbors list when they go shopping. Someone with 10 to 12 items will be first in line vs someone with 1 or 2 items will be at the bottom of the list. Whenevr there's an event going on I always make a lot of money. This last event I started out with around $155,000 and by the end of the event I had over $310,000.....and I spent a ton of money myself buying items to send out on deliveries to get the tree parts to earn the cat. It does get easier once you get more buildings and expand the shop. I'm level 46 now and I remember I struggled for cash up until I bought the pizza oven and juicer. Once I got those and started focusing on selling rather than leveling up the cash started rolling in.
Don't try and get to level 60 as fast as you can. The more you level up the more cash it's going to take.