Thanks a lot for this info, athanaric and TheLastDays - it helps

I might have been not clear enough, so just some more words:

Cities’ income: I knew that the number under the town model on the strategy map misleading and I didn’t mean it. I meant the numbers you can see in the city scroll – trade, taxes, mining. If you look at them the income of a big city is still very small compared to the income of a small town.
What I am relly interested in is: what is (if any) the link between
• population and farming income
• population and tax income
• population and trade
or cities have defined numbers for above and you can increase it only through buildings?

Some outstanding questions – maybe somebody other will know:
1.2 Cavalry charge: How quickly does the “charge bonus” dissipate - 5 seconds? Ergo: when should I order a unit to withdraw after the charge? Or maybe I can see some graphical effects?
2.2 Friendly fire: so you never put slingers behind a line of infantry? You put them in front?
4.1 Hiding in the woods: Assume that my units hide in a wood and I want them to go through the woods to encircle the AI troops. Will the AI spot this move instantly, or only from a close distance? Does it differ for cavalry and infantry?
6.1. Government bonuses: Where can I read what are the benefits of different govt buildings? In this thread somebody presented SPQR/Seboz/Makedon – where can I find this data?
6.2. Where can I read about relationships: loyalty <> public order <> happiness?