How do you think wine production at the Arbor is managed? Do the Redwynes own all the vineyards and manage distribution and sales, or do they just tax farmers and merchants?

Great question. If it’s anything like the standard manorial system from Medieval Europe, it’s probably a mix – the Redwynes hold the best lands themselves and either pay or compel labor to work it, the rest gets leased out to peasant tenants who pay rent most likely as a percent of their harvest, and the Redwynes probably own much of the production process (the presses, the cellars for secondary fermentation, etc.) both for themselves and (for a fee) for their tenants. So they probably make their own, get a bunch more in taxes from their own peasants, and from their vassal lords and knights. 

What we do know is that the Redwynes directly market a lot of wine – because when you need a thousand merchant ships to move your product, you’re talking some serious volume. There’s a number of ways this could work – it could be that the Redwynes just hold a lot more of the land directly than is the norm because of the advantages of centralizing production, it could be they have the right of first refusal on all wine grown on the Arbor or some other form of monopoly on distribution and sales, etc. 

This also explains why the Redwynes are so keen about excise taxes – much if not all of their revenue comes from wine, both in the production and commerce phases, so keeping those excise taxes down means pure profit on their end.