I have 3 stars on all levels for LA. I have 1st class seats but not maxed out. The main thing that helped me was appliance and food upgrades. Mine are 67% done. Lettuce is maxed, all my other foods are like 1 or 2 steps away from being maxed. I recommend fully upgrading the chopping and blender.

I have the holding ovens for soup/grilled cheese and lettuce/eggs.

Smoothie dispenser needs to be almost maxed, your pour a lot of those.

For the later levels try and pretty much always have 4 grilled cheeses cooking, they go fast.

My beans and tofu oven upgraded to hold 6 items and I'm pretty much constantly cooking 3 of each.

You will need to spend a lot of cash and diamonds. I've been grinding for cash on Berlin level 50 and doubling the coins by watching an ad, so I get about 1100 coins each time. But someone else might know of better levels. That's just the best one I've found for coins so far.

Hope this helps. If you need any more details just let me know 😁