Apparently everything in the game is RNG. Matters little what we do, diplomacy-wise or otherwise, it's a crapshoot.
If an AI declares, reload and more times than not they won't re-dec (or the reverse).
This is a very strange design decision for a 'strategy' game. My guess is that RNG is easy to program, and 'intelligent' choices (such as 'if player does X then AI does Y' is time-comsuming. Or maybe it's because 'strategy' games 15 years ago were mostly RNG. Or both...
If the AI were completely deterministic, then it would also be completely predictable. How I suspect it actually works, rather than being a pure crapshoot, is that the state of the game world and your actions are used to set the odds of the AI taking certain actions. What you do, diplomacy-wise or otherwise, does matter, it's just not 100% decisive.
1. I don't play on Expert, but it is the same on Challenging too.
Strange... I play on the difficulty where the AI first starts to cheat a little (one step past Challenging; "Hard", I think?) and have never seen an immediate declaration of war by the AI. On the contrary, unless their faction power rating is substantially higher than mine, I find them rather sycophantic - even if they're from the opposite Kingdom/Empire alignment, our relations tend to drift upwards and never come back down, no matter what I do short of starting a war myself.
6. Press V to send all of your units out of the city. There are several hot keys, not mentioned in the manual. This is one of them.
In my experience, that usually works, but there are some cases (I think they're related to the city being adjacent to coastlines, mountains, or other impassable terrain) where I can hit "V" all day and nothing will happen. But I don't really think this "select all" request is entirely a city-related issue, multi-selecting units should be reworked in general. As it stands now, the only way to multi-select is to hold ctrl or shift, which makes it a bit of a nuisance to deal with anything other than the extremes of either just one unit or the whole stack.