Yeah, the Mage Retreat is definitely perfect for that. My main concern is, access to extreme outcasts and/or villains to alchemy, especially scheming wizard types. A mad scientist type NPC in the Drain would suffice, surely. In response to the lack of store in the Fishery, it's not necessary. Supplies are obtainable, it's the bench that is needed and are hard to access ICly with outcasts. Also, it'd make for great horror scenes down there:
The man with the cold gaze gives you one last freezing glance, before pulling on a pair of thin leather gloves. He walks calmly to the table before you. Strange instruments, glistening, bubbling, boiling, froth at the table. Odours bitter and sweet pour from the glass containers, and alien things float in stasis in slime filled glass containers. The man with the cold gaze picks up a beaker, and looks back at you curiously. With a wicked grin, the man takes a coin from a pocket, and drops it in the beaker. It begins to fizz... Moments later, the coin is gone. He approaches you slowly, the horrible substance clutched casually between his gloved fingers.