Usually DLC is hinted in dialogue of the recent one. I've seen a couple of stuff that talks about Elsweyr, like after the Burnt Branch quest and a couple of Khajiit in Lilmoth. I'd like to see Elsweyr, especially the Tenmar Forest or Orcrest.
No, the Kinlords/Kinladies rule the other major cities like Shimmerene and Sunhold. Alinor is the exception. There was also High Kinlords/High Kinladies in Skywatch and Firsthold, but that title hasn't been used again and whether it actually overlooks the regular Kinlords is unknown.
I think Vicecanon is just another type of leader. This from the Emperor's Guide, "Until, that is, the rise of the Argonian Vicecanons, who seem to fulfill the administrative functions that councilors and tribal leaders do in other realms."
High Elf leaders are usually High King/Queen (Alinor), the Kinlords/Kinladys (other cities), and the Canonreeves (minor settlements).
Wood Elf leaders are Treethanes (cities/minor settlements) and Kings/Queens (Capital)
Khajiit leaders are Lords/Ladies and Clanfathers/Clanmothers, also probably Kings/Queens
Probably Throw Voice. It'd be fun to mess with people with that
There is a third faction, the Lhotunics, who are a middleground between the Crowns and the Forebears. We don't hear much about them which sucks, but they were important in Hammerfell around the time of the Oblivion Crisis. I'd honestly go with these guys or the Forebears,
The stuff around House Ra'athim, who are a Dunmer noble family from Ebonheart. There members have been well-known leaders like Barenziah and Katariah. I think there should be more of them.
It's not bad, it reminds me of this.
Sure, that'd be cool. This page might give you inspiration. Tamriel has it's own version of Halloween called the Witches' Festival.
The Imga are all apparently in Falinesti (Valenwood capital) which is also gone. Maybe in future DLC we will see the Imga in Falinesti.
The Thalmor is the leading figure. It consists of various leaders of the provinces (Altmer Kinlords, Bosmer Treethanes, etc.) that work together to govern the Aldmeri Dominion, kind of like the United Nations.
Cloudrest is scaled to your level like everything else, so you're fine.
I imagine having plans to build Anumidium would be something that was swept so far under the rug. If one person found it, I'd imagine that they wouldn't tell anyone about it, because that's something someone would kill for. And the Telvanni aren't the type to trust their own people. I like to think one maniac found it, and took it away to try and rebuild it, with what little they have. Jumping ship to ship from Tel Vos, and all throughout Tamriel to build this weapon, taking years to build the machine.
Hammerfell would probably be a good place to build it, to get away from big powers, it would make since that the plans would be in Morrowind, where people would try to find it, rather than the other side of the continent. It might be built in Volenfell or Fang Lair, both former capitals of Dwemer Clans (Rourken and Kragen). Hell, the Kragen were the ones responsible for the Aetherium, so imagine seeing Numidium infused with some Aetherium. This person, who managed to find the plans would probably hide away in Hammerfell, to construct the Anumidium alone, but since materials, like a power source would be difficult, it would take them years, until his dying days to finish building and working it. This would be a good Daedric Quest for Hermaeus Mora, because this is some powerful knowledge, one that would be in heavy circulation because, as far as I know, there's only one copy. And the person would be super paranoid and try to kill anyone trying to stop them.
It think it's either Mehrunes Dagon or Peryite, where it would be a world of constant suffering. Coldharbour is depressing and cold, but I see it something that could be taken use to, whereas a place of utter chaos or agonizing disease sounds worse.
This wiki comes in several languages, albeit not with the same amount of content. I think it depends on how big it is in each country. This is a list.
The Elder Scrolls has it's own version of Halloween, in the form of the Witches' Festival. It's not on the 31st, but it's close. It's on the 13th, which I think is a node to Friday the 13th.
There's no information regarding Daggerfall, in general by the time Skyrim happens. The latest on Daggerfall takes place, pretty much a year before Oblivion happens. King Gothryd ruled for thirty or so years, and he married the princess of Sentinel, Aubk'i. There's no info whether their family still rules in Daggerfall but that's the latest info.
Assuming it's Hammerfell, the main character would be the HoonDing, who is pretty much the hero of Redguard legend. They appear whenever significant change occurs to the Redguards and Hammerfell. Cyrus from TES: Redguard was supposedly a HoonDing, while Frandar Hunding was definitely one.
The name "Elder Scrolls" didn't mean anything, it was just a name that the Arena designer, Vijay Lakshman created out of nothing. It stuck because it sounded cool, and it does. It was later given context. Here's a source, an interview from Ted Peterson. This is pretty much why the Elder Scrolls don't serve any in-game purpose.
I use to be all for Valenwood and Elsweyr as one setting, but then I realized size doesn't matter and they could just scale it to be much larger. I would like to see Valenwood as a setting and have either Auridon or the Elsweyr-half of Reaper's March as DLC.
As for a story, I think a rebellion that would attempt to expose the Dominion in Valenwood would be good. The Blacksap Rebellion in ESO was created to go against the Dominion so I could see them come back, and the Silvenar could conspire against the Dominion from the Shadows, all for the benefit for the Wood Elves.