I like your plan. I don't have much practical experience on useful plants, other than my reference works. I only know and recognize a few, so I can't help you there. However I have a few ideas for the extra 3 work stalls.
Coppersmith & tinsmith tools & equipment
Optical products tools & equipment
Mechanics tools & equipment
Wood working tools & equipment (finish work, furniture & cabinetry)
Cobbler/saddler/harness maker's tools & equipment
Cooper's tools & equipment
Wheelwright's tools & equipment
Gunsmithing/reloading/bowsmithing/arrowsmithing tools & equipment
Attached open-air blacksmith area
Metal forging tools
Metal casting tools
Ore smelting tools & equipment
Mineral/earth/rock products processing shed
Lapidary work area w/tools & equipment
Flint/obsidian knapping tools & equipment
Gold & silver working tools & equipment
Petroleum products refining tools & equipment
Natural Remedies Apothecary
Masonry/stone tools & equipment
Pottery & ceramics tools & equipment
Glass making tools & equipment
Chemical lab
Biology lab
Medical lab
Physics lab
Optical lab
Electronics lab
Black powder production shed
Acetylene production shed
Oxygen/hydrogen production shed
Candle making tools, equipment & supplies
Fabric, cloth, & rope production tools & equipment
Tanning, leather & furrier tools & equipment
Quill making tools & equipment
Glue production tolls & equipment
Ink production tools & equipment
Paper production tools & equipment
Basket-making & other plant weaving product tools & equipment
Plant oil press
Rubber rendering, molding & curing tools & equipment
If you are interested, I have a long list for a self-sufficient estate much like you are talking about, and from which I took this list. Just PM me and I can make arrangements to e-mail it to you.
Just my opinion.