So it looks like lots of individual adventures. Are the portals always/regularly up and to the same places, or is where to go next out fo the character's hands?
As this well, you have a really in-game reason to allow any races/classes/etc. Heck, two players of the same race could be from different material planes and have different cultures and such. Lots of freedom. And the flip side to play with their expectations - you referenced Sliders and that did it some times. I remember one about the men being shirtless as a big crime.
The idea that they aren't allowed to own anything in the Well - does this mean that they need to keep separate equipment cache's for each realm, and anytime they go someplace new it's weaponless, armorless, material-component-less?
Question - is it just wealth, or do the patrons also gain fame and bragging rights? You could have a whole thing about betting on various expeditions by patrons, rival expedition teams that you can meet up with in other realms and may help you or may steal the idol from you, that sort of thing. And another layer.
Portals: How the portals exist, when they came to be and why they are is not something anyone knows, although the citizens of The Well believe the Kumpali is responsible for some part of it, since He has control over them. The records of the city itself are so old as to be impractical to study or teach past a certain era, and the Realm itself is unknowably old. Any anyway, knowledge is the purview of the Kumpali and the wealthiest citizens only.
Races/Realms: Yes, the players have full control over the people they come from. One of the rules of the game is that each time you level an aptitude, you write down one fact about either your character's history or about the Realm they come from. Thus PCs that survive longer will develop more information. And even when a PC dies, the facts recorded about their Realm can live on in a new PC.
Property: They are allowed to own possessions, just not landed property inside the boundaries of The Well itself. If the players can manage to find it, they can rent property for storing possessions. The city is incalculably large and dense, so even just navigating it is a challenge. It is so bustling and dynamic that a bevy of shops can appear practically overnight blocking an alley or street that was open before. They city itself takes on a life that can't be controlled, but still the profit runs in and through and keeps it from complete chaos. Also the fear of the Kumpali's power.
Patrons: Wealth is the primary goal of any citizen of The Well, including the Szesci (Patrons). Nobody would be mad enough to want to reside there (or do any business for that matter) unless they were primarily focused on acquiring wealth. Of course there are those born there who are part of the great system of cogs that make the lower economies churn. That being said, any given Patron may have secondary motivations, or their presence in The Well could be a front for something more sinister.