I normally leave 1 Militia troop behind, and if I don't have I leave 1 infantry. Never tried with AA, though. I think they're too weak, but give it a try and report back

This is what i do when i capture cities and provinces. If the province/ city is touching another nation i will leave either 1 inf/militia or 1 AA gun. So far i haven't had issues using AA guns to keep a city from rebelling. If the province/city is surrounded by other captured provinces i don't leave any troops. Ex. When i toke Warsaw from Poland as Germany i didn't leave any troops to keep it from rebelling but when i toke a province touching USSR i left at least 1 inf or 1 AA gun. The way i understand the rebellion system is when they rebel they go to another country or the original country, but i've notice that the only countries that rebel and go to other nations are those touching the other nation or are a sea zone away from that nation. Like Crete going to UK. The only option i see provinces rebelling to another nation is the original nation but only if the original nation has a province touching the rebelling province.

Examples:


The No Rebellion province is surrounded by already occupied lands so it will never rebel to another nation
The Rebellion province is touching 2 nations so i will rebel to another nation if overpowered or not defended.
It could go to Germany (the original owner) or Czechoslovakia which is bordering it.

So...only border province and cities have higher chance of uprising when neighboring with other countries.

Its not completely proven but this is my observation that provinces will only rebel and proclaim to be another nation if they are some how bordering or a sea zone away. I still dont know how many sea zones.

Well,
In Supremacy1914 it is possible that non-border pronvices were uprising and changed their owner. And it didnt even hat to be a neighbour, so there is possibily (I dont know how high it is) that a non-border Province changes his owner to one, which is far far away(extremly rare and very unlikely to happen to you).
For example, Warsaw couldve revolted and joined Italy.

About how high the chance of an uprising is, well, I dont know. If you look at the provinze morale(just conquered one), you can see the chance of an uprising. And the more streght of units(!) is in the province, the lower will the chance be.
Even though, I didnt left any troops in new conquered provinces (Chance of uprising ~30%?), only very few (1-3) did join another nation(I had at least 20 border-provinces with a chance to revolt unprotected).
In conclusion, I think any protection against revolts is useless, unless its an important province/city.

After taking a few provinces, I have observed that the chance of uprising is 30% if unprotected and 25% protected.
The chance decrease depends on the army strength occupying the province, the lowest I got was 16% occupied by infantry, armored cars, and a tank.

The success of the uprising and the chance surprising it depends on the occupied force and certain circumstances, if close to the capital and surrounded by frendly territory you can leave it undefended (especially if it have little value).
I once occupied an African province of a population 1k people with 2 militia units under 80% effectiveness, they rebel in the end.

If the province do rebel they will desert to the nearest territory other than your own. The African province that rebel againts me became Spain, even though spain is a bit far, and have a small colony near it so it became a candidate to desert to, once more when they desert they join not only the closest but the biggest or strongests. For the same example the African province became Spain and not France because france was already defeated a week ago.

That's all I have observe, these things are not yet tested so don't take this as fact, take it as an educated guess.

I think the damaged buildings just stay how they are
This is how I "noticed" it, i took over a province, and if i didnt like to rebuild the building, it just stays so.

The only possibilty is, that the building will be destroyed and be gone. But I doubt that

If you capture a province with buildings on it you have to spend resource to repair them like supremacy, what you think buildings repair themselfs?

The amount of resource it needs for repair depends on their damage state but you will not spend the full amount like you build a new one.

In short no, buildings can't repair over time and you need to repair them with resource, it is very hard to consolidate on new territory since you won't be able to generate a lot of resource out of conquered territory outright, also if you capture a city you need to spend a lot to use the industrial complex in it. You can however train militia units there for defence.

You can do more than build militia units in those cities. Some cities will have upgraded factories which don't cost crazy amounts of resources. The only buildings that are crazy to build are lvl 1 Factories cause they require 5k rare materials. Since rare materials are hard to get unless your Sweden. This is a issue with expanding early game late game is much easier since buildings will be upgraded. This usually implies to AI nations or Inactive players. Since normal players will upgrade their buildings as soon as possible.

You still need to repair them if you capture one from an enemy city, least it does not cost 5k

About the sea zone distance ... Last night I lost civitavecchia (Italy) to Spain !!

I had just re-conquered it from Yugoslavia and couldn't really afford to leave troops in it.
But I was shocked to see that I lost it to Spain.

Ps. There was no land connection, just sea.

A land connection is not required.

I know, I was referring to the unknown sea zone distance.

Especially taking into consideration that Spain isn't just around the corner.

Is Palma nearby by sea?

I don't know but I ussually use 5 units to be sure.

you lost a province with 2 infantry?
i lost a province with 2 militia after said militia conquered half of Africa.