Please explain the economy of a Seasonal vs Legacy Character

I understand that a seasonal character is brand new, fresh, no stash no resources etc. Their economy is tied to other brand new seasonal players so everything is fresh.

My confusion lies with the option of Legacy. Lets just pretend I level up a character today and its level 50 on April 2nd and I go with the Legacy option. I can now make that character the new spec right (such as heartseeker etc), but how does it work with my inventory/items/stash/resources and the Merchants Guild in particular? I need more than "legacy is separate," please. Are the legacy players ONLY trading/purchasing from other legacy players? Essentially there are two separate auction houses?