1 - Achievable for coop war requests with some work, already the case for DoF requests. Trade deals can be made the next turn unless the AI has traded whatever you want away already (delayed responses on trade offers would open a number of potential exploits, although it's not impossible). Don't think there's any other statements where this is important.
2 - The reason for the AI asking only when they want specific things in trade (and for cooldowns) is to avoid spam. If every AI had a trade offer every turn, it would become chaotic. The ability to gift units to major civs was removed in VP.
I could look into a system of giving more hints at how to improve diplomatic relations, but again, there can be a lot of civilizations in a single game and if all of them popped up to tell you what they'd like frequently it would be spammy and annoying. If there was a better way of conveying this information, then perhaps.
3 - I've proposed on Github that we add a button to City-States to cancel/stop all quests, to prevent unintentional Influence gain.
4 - The AI keeps some of this information hidden for strategic reasons. If you can see that they have an enormous negative modifier because of your warmongering, for example, then you can more easily deduce when they aren't really FRIENDLY. If hidden modifiers and invisible number scores are an issue for you, there's already Transparent Diplomacy.
There are a couple dialogue options that could use a mouseover popup to explain the diplomatic consequences. I'll add that to the to-do list.
I'm not sure how else it can be made clear - I suppose raw Opinion numbers could be added to these popups, but I think that would cause confusion for players who aren't playing with these values visible.
5 - This is too vague to be actionable. Are you proposing a mass joint war, or...?