How are they represented in game?

Do they own settlements or buildings in other people's settlements?

They own settlements. In some temple settlements, they rent space; in others, or in neutral territory, they set up garrisons that accept their presence.

Do they have faction guards?

They have faction guards, clad in Bonemold armor of various styles. There are also Watchmen, who act as scouts and patrols, but are not technically faction guards.

What notable holdings do they have? Where is their seat of power?

The current seat of the council is Ald-ruhn, the traditional one is Baan Malur, where much of the bureaucracy remains. Other notable holdings are their march capitals (Ald Iuval (Water), Kogotél (Ashes), Kartur (Stones), and Soluthis(Snow)).

What active border or holding conflicts do they have?

Aside from the Nail-Knock Reavers and the Marakh-Bazhul Orcs, the Redoran have also latent border conflicts with the Hlaalu.While it is heating up in Vvardenfell (with the conflict against the Telvanni a secondary theatre), the situation of Ald Iuval and Marak and the Hlaalu mercenary company in Cormar (the district capital of the Empire) are sources of conflict as well. Bodrem is another important focus point, akin to Caldera. 

What other factions hate or love them? Why? How is that represented?

The Temple likes them (up to having them act as garrisons for pilgrimage sites and cities), as do the Indoril (who often have some presence in each other’s territory) and they have the grudging respect of the Imperial Legions and the Fighters Guild, as well as the Marakh Bazhul Orcs (they see each other as a fair and worthy opponents). A lot of buoyant armigers come from Redoran territory and the two factions work well together.
Relations are neutral with the Dres (cordial but with resentments over the Arnesian War), Nords of the Velothis and regular Orcs. They are outright bad with the Hlaalu and Telvanni (although in their case, they are simply too far away to have seriously clashed), as well as with the Nail-Knock Reavers.

Which of their members is an Elder Council member (Red or White Chorus)?

They have no members in the Elder Council.

What is the player's experience with them?

Purpose: What do we actually want to achieve with this faction? What do we want the player to experience with it? Why is it playable?

The Redoran questline should be the closest a player comes to experiencing open warfare. It should portray an honorable warrior society on the decline, as the Redoran never really had a place in Tribunal society (particularly after the Armistice) but which is still capable and willing to be a force to be reckoned with when its shackles are lifted.

In short: Honor! Klingons!

Format: How can we best deliver the experience to the player? How should the quest content be structured? (Disconnected quests, a coherent storyline, etc.)

The questline should start with disconnected quests while the player puts out local brushfires. It will eventually become fairly linear with the Nail-Knock Reaver uprising. The Vvardenfell questline should be fairly disconnected, but have some “meet the boss” kind of moments - and the player still needs a patron from the council… on Vvardenfell.

Content: How should the faction gameplay be distributed in the gameworld? e.g. Locations for misc quests, low/mid/high-level questlines, etc.

The March council halls provide early quests and advancement, high advancement goes through Ald-ruhn (how exactly this will work can be figured out later). 

The later Nord uprising quests might start from temporary military camps set up in (re)conquered strongholds as House Redoran pushes the Nords back.

Implementation: How can we most practically go about implementing the gameplay? One claim, several?

The low-level questlines can be their own claims, the uprising questline (and mainland stronghold) should be its own claim.

What is the future outline?

How is the faction represented in the vanilla game, assuming it is?

The Redoran have several settlements and a house questline. Their council is located in Ald-ruhn with no mention of the situation on the mainland, save that Bolvyn Venim, as the head of the house, moved the council to the Skar.

They are engaged in a variety of conflicts with the Hlaalu and Telvanni (who they also collaborate with against the Hlaalu), and there is in-fighting among the councillors (Venim is a controversial figure who has resorted to kidnapping to increase his influence) and the Mad Lord of Milk, who resorted to banditry. They are also working with the Buoyant Armigers and the Temple in their conflict against Dagoth Ur.

What is the rough outline for a faction plot?

The player initially gets involved in vanilla-style disconnected questlines in the march capitals, largely involving conflict with local Hlaalu. Then (most) locals Nords rise up and the mainland questline focuses on overcoming the uprising, the player gaining an increasingly prominent role in the conflict, and gaining a stronghold on the north coast in the course of the conflict. The player will also need to seek advancement and eventually a reckoning with the Redoran leadership on Vvardenfell.