The way I look at it, each of the Estates on Sclaras is prolly akin to a "Castle Amber" - not as big, prolly ("Castle Amber" is very large, as large as, well, the Palace of Versailles upon which it is based; I doubt any of the buildings on Sclaras are that big, though many are more than two stories high), but in the sense of being unique & bizzare, with excentric mages and their excentric family members & servators, guardians, odd rooms & features, and the like.
I also imagine that each Estate is somehow sectioned-off from the others, by hedgerows and/or a line of trees, probably with some sort of defenses (primarily detection stuff, to provide an "alert" when someone crosses the boundary of one estate to another). Entrances are probably gated (iron gates & fences at gaps in the hedgerows). I prefer the hedgerows thing to walls as such.
The prime properties are ones along the coast, with a "beach", but the island itself rises above the sea, with cliffs on all sides (except a small low area, a few acres in size, which functions as a harbor/port for the isle, with docks, and is a "common area", a port of entry for visitors - who, of course, must be invited by one or more of the residents. This area is also where some trade is conducted. The best analogy I can think of at the moment is Skullport in Waterdeep, though not *quite* as seedy and illicit). The rest of the island is: a narrow beach, probably 30 meters/yards or so in width, forming a ring around the isle. Beyond that the island rises sharply, with chalk-white cliffs. Atop those are the estates proper. The seas around the island is riven with reefs and rocks and other things hazzardous to navigation, and the wizards aren't beyond "seeding" the waters with dangerous critters as a deterent to interlopers. This isn't done in any coordinated fashion, each wizard does whatever they want when it comes to this, and it can lead to the critters put in place by one wizard getting into bloody fights with those of another, eating each other. This is often an occasion for "sight-seeing" among the population of the island, when a particularly good "bout" starts (another expression of the Thyatian proclivity for gladiatorial combat). Strange, often enchanted, fogs surround the island beyond a few miles, limiting visibility for ships sailing to it. The area immediately around the isle is almost always clear, but there is a "donut" (or begel) of fog with the island in a "hole" in the middle.
The skies are also dangerous, as all the wizards are keenly aware of the possibility of trespassers coming in via this route. Indeed, each Estate tends to be protected multi-dimensionally: surface, air, underground, and trans-planar, especially from Ethereal infiltration & observation.
None of the Estates are huge, but with 160 acres (aproximately) they aren't tiny, either. The current inhabitants aren't the only Wizards who have lived here - remember, Valentia is said to have been the first Estate-holder here, almost a thousand years ago. So there has been a milenium of development and cross-development on the Island. Many Estates have not only the villa/tower/whatever-the-heck-they-want-as-an-abode of the current inhabitant, but those of previous inhabitants (when the current or some prior occupant decided not to use that one, but to build their own instead). Some of these have been torn down or are in ruins, but usually not everything has been removed. The Wizards themselves often stumble upon enchantments or dangerous areas, especially underground chambers, left abandoned and lost by previous residents. They often don't want to be bothered with "clearing" these themselves, and so will hire outside agents (Our Party of Adventurers) to do the job.
The Wizards also often need specific items for their experiments & researches, and so will hire agents to procure it. Many are also involved in feuds and rivalries with their neighbors. Almost always, these are not deadly, but involve "liberating" property or "counting coup" against them in some fashion. Adventurers are hired as security against such efforts, and also to perform such feats. Some of these can be very bizzare, the rationale known only to the people involved, not to those hired by Wizard N to, say, plant a pair of neon-green bloomers in the bedchamber of Wizard X. Things can escalate to the point of fabricating research, sabotaging research, stealing this or that item, and other things intended primarily as embarassement. Assassinations, however, are almost unknown on the Island - by tacit agreement, as all the Wizards are aware (from sad experience, it must be said) of what can happen if scores of powerful Wizards engage in blood-feuds.
This isn't to say there aren't (occasional) duels among the Wizards, but they tend to be kept to a minimum, and in those cases people are not hired to perform the job - they do it face-to-face. These duels are almost never to the death.
Wizards being Wizards, some residents have been around since the early days of the Empire. So they have long memories and are often seen as a source of information. The Wizards aren't really patient with outsiders, though. If and when they want to meet with "the general public", they'll travel to Thyatis City (for example) or elsewhere. Visitation is by invitation only, and uninvited guests "sleep with the fishes". If you don't hear back from someone who went to Sclaras uninvited, don't bother asking anyone who lives there about their welfare and whereabouts - you won't get an answer. Some are killed outright, a possibly merciful death, while some are put to other use (they being seen as "finders keepers" property by some mages who want experiment subjects). Merciful wizards might just wipe their minds of memories of the isle and deposit them on another Plane with a warning to never return again, as they might not be treated so kindly.
As for the Estates themselves, as mentioned, they are as varied as the Wizards who inhabit them. The hedges & tree-lines are used to provide privacy. Each Estate might have a "atmosphere" far different from another, and some are very artistic in establishing a "theme" for their estate. Some are dark, foreboding abodes, others are sunlit and park-like. Several are forested throughout, some being maintained in a tropical, others sub-tropical, and still others in a temperate climate. Some do not have man-made structures above-ground, others have "traditional" towers, many have villas that, from the outside at least, are not unlike those of wealthy Thyatians on Carytion or in the Duchy of Thyatis. Before the Week Without Magic, there were even some that could only be maintained magically (floating towers, parts of buildings that were connected only thinly to the ground with magic being used to support the structure, odd-shaped buildings that likewise needed magic to keep them from collapsing, and the like), but these didn't fare well on that day and for the most part haven't been rebuilt in that style. With 250 Estates, only one's imagination limits what any given Estate and its inhabitants might be like.
I always felt that Sclaras was a silly place for retired Magic User NPCs. I thought it had much more potential than that though, as an Island that was home to a large number of powerful isolationist Wizards.
I pondered on the idea of making Sclaras home to a wizardly order like Tokien's White Council, which would for the most part stay out of worldly affairs, except for the occational Grey Robed wizard who had an unhealthy interest in such things, but would get involved when it really mattered, in the major conflicts between good and evil or whatnot. When the Wizards of Sclaras got involved, you'd know it was serious!
Maybe the Wizards could be something like the Vorlons from Babylon 5. Most of the time, they would stay on their island, only letting very few visit. But sometimes they would offer advice on political matters out of the blue, in a way that only a few would suspect that their actions were part of a much bigger picture. Perhaps they would also have an ancient enemy and that they are just waiting, preparing for that enemy to make the first move....
Just a couple of ideas.
Havard
But kewl ideas.