A couple of issues I haven't seen mentioned: humidity control and noise abatement. (Tennessee might be a great place to hoist the Gadsen flag and run Mozambique drills in your backyard, but even "stick" homes have condensation issues here.) It definitely might affect the other half of your business in terms of materials storage and the like. (FWIW, while we're all naturally focused on the issues of darkroom design, I think it might be the logistics of your equipment manufacturing that will be the toughest to accommodate to kinds of spaces that have been discussed.)
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