The tooltip, when you hover over your Balance (on the Topbar) actually displays your GDP as Net Income which is giving you the impression you should be gaining BC per turn when you are not, just a bit of miss information atm (untill they change Net Income to um GDP). 3.0 Economy (non synthetic) is all about Tourism (main income) and Trade (side income), without either you will struggle, with only Trade it will be a chore to balance your economy, Tourism is a must atm.
For max income, get as many Tourism improvemnt on you homeworld as you possibly can, preferable all hub'd together for the adjacency. I have hit 7k+ per turn doing this. (With port of call on all other planets)