Hi BobbyJane,
["How about too few towns and some towns not placed next to a river that could have been?"]
"Ok, maybe I should've focused more on settlers in the beginning, but I had 2 settler factorys? Not enough? Do I need 3? Then I will be low on defence and my whole empire will crumble with a single small attack in the beginning. Hmm, but I did only use wa-s-wa-s. Is wa-wa-s-wa-wa-s better?
Tsingtao is the only city I could've placed by a river right? I should've I realize now.
Should I just forget to plan big cities and make a tighter build? Is this a requirment for surviving on this level?"
Canton should have been CxxxC and then it would be on a river. Then you could place another town CxxC or CxxxC from the new Canton site. Tsingtao should have been CxxxC from the capitol and on the plains on a river.
I do not even need settler factories perse. I make no effort to create a settler factory. I may defacto have one or more, but usually not. I make settlers where I can and how many I can use controls the rate.
On a larger map on would be more inclined to dedicate a town or two to settlers. Later I may be making settlers in a number of places, if I am taking towns fast enough.
You are never low on defense, you are either weak or strong. It is an offensive calculation, not a defensive one. I prefer to put them on the defense.
["How bout 21 defenders and only 11 attackers?" "Why is a border town held by 1 archer and 2 cats?"]
"I should've posted the save before the fight

It was a gruesome battle with many men lost, that's why there's only 3 units left in that city and that's why I gave up and restarted. My city farthest to the east is an example of how it used to look

"
That could be a valid reason, except no units are on their way to help out.
["How about 11 workers for 12 towns, each with lots of land?"]
"I create 1 worker per city, that's good right? (1 worker was MIA) I need a huge army just for defending my lines, becouse I am low-tech, so I don't really want to spend more on workers, should I?"
How many workers is a function of the work to be done. The wider the towns are spaced the more workers per town is required. 10 towns at CxxC yields fewer tiles to improve than CxxxxC for 10 towns.
You have much of the land improved now with the 11 workers. The only reason that is true, is that it is 430AD. You have been some what stagnated of late and so the workers caught up.
The likelyhood that those workers could have gotten the tiles being worked improved as fast as they needed them is low. IOW I would bet that many tiles were being worked without improvements in the past.
That is the gauge to use on the number of workers you need. As long as your citizens are not working unimproved tiles you are fine.
"[You are in Feudalism, so that had to be recent, why? "]
"When I got attacked I needed allies and that could only happen with a Gpt arragement, so I didn't have any money to buy either monarchy or republic, and since I only had 2 cities and the rest towns I could get more free soldiers with feud."
What I really meant was not so much why Feudalism, but why no government change earlier and then there would be no need to switch to feud.
Feud is a form that is for specialist use imo. You either are going to be a warmonger or not. If not then Repuiblic is the first and best choice. If war is the answer then Monarchy is the ticket.
That choice needs to be first on your mind and you sort of beeline to the one you selected.
In selecting allies you need to consider the impact. The thing that I consider is that a very weak nation is not going to help me and could hurt me as an ally. This is due to the likelyhood that one of the stronger enemies will take towns from them and get even stronger.
This does not help me. Yes they may join the fight against me, but then they are weak so why worry? My first worry is they will lose towns to the others and promote their units and even give them stuff to end the war later. So I prefer to let them either sit it out or fight me.