So here it is:

Design your foundation as if you were using it for commercial flight, but use normal deviation first and build in the building at least 4 Shops and 4 Cafes, all 8 with 250 square meter and several fridges and shelfes (6-8 in each shop/cafe depends on the contract). This will make you around 20k/h. Even during nights!

With this setting you play the extreme difficulty as if it was a normal game.

In my view this is kind of a cheat, but I wanted to share with you you nevertheless.
This might not work for later versions, but for Aplha 21 it does. Maybe the developers restrict that you can have 3 star shops/cafe from beginning.

The developers seems to have changed it a little so it is not that "easy" now. If you want a complete guide on extreme difficulty please visit my new guide:

https://steamproxy.net/sharedfiles/filedetails/?id=1773241673

Gruss seturo