Farmtek is solid. S1000, S2000, they can stack them together, custom engineer, custom fabrication, whatever you need assuming the order is big enough and you're willing to pay. If you're thinking about stacking together 20 acres of greenhouses, unless you're on perfect level ground, you're going to have to adjust for elevations which might need some custom design work to fill the transitions or brought to grade prior to expansion. Farmtek's manufacturing facility is out of Iowa.
Conley's was a bit more expensive and never was as responsive or as flexible as farmtek. Met with them, and seemed knowledgeable, just didn't hit it off quite as well and higher cost for the same/similar items.
FF seemed too gimicky, and higher cost as well. But they were years ago, maybe they've changed.
No experience with the other manufacturer.
Industry standard, might not be the best option. I see plenty of open span greenhouses, 30ksf+. Check out some of the Canadian producers that are doing massive spans. However, Canopy just had a complete crop failure in one of their facilities (over 1Msf, https://greencamp.com/canopy-growth-...e-bc-facility/
). The problem with large spans is the potential for pathogen spread and the cost to maintain with IPM. Smaller isolated bays cost more up front in construction, but the savings on IPM when needing to spray something specialized is a fraction if only needing to hit 1/20th of the facility and proper biosecurity is used throughout to prevent cross contamination. Plus fine tuning environmental controls to the specific maturity level. You have to decide what is more beneficial there in regards to capex and ongoing/longterm operations.
Go with separate veg/flower houses for sure, instead of splitting up single greenhouses. You want to be able to close up a house and nuke it at the end of the round in case of pests or pathogens, and if there's always plants, you can't do that. Plus climate control for end of cycle and veg should be very different, and you're not going to have different zones in the same greenhouse (more zones, more cost, more wiring, more equipment).
Who are you using for climate controller?? Farmtek will suggest LINK4, but I'd suggest to stay away. Had very good success with Wadsworth, they'll just need all equipment specs and have the SEED controller which is nice and upgrade-able as you continue to build out. Not cheap, but all climate features, lighting, weather station, light dep, vent/circ fans, heaters, etc.
HEPA filtered air?? Assuming you're running wet walls, would be interested to see how that would even be possible. Each greenhouse will likely have intake along most of each endwall, and unless prefiltering into an enclosed walkway, doesn't see massive air filtration being feasible... Greenhouses have cracks, vents, bugs/pathogens will get in eventually even with all the insect screening and prevention one can muster.
CO2, nice for night if you need to close everything up, but otherwise not quite as useful. Burn propane/ng for your heat and you'll generate CO2 as well. I'd love to see a greenhouse that could execute it well, but with air exchange being the main source for cooling, a lot gets wasted unless really fine tuned.
What about post? Dry/cure, trim/package. Extraction. Infusion. Storage. Depending on the state/country, other rules/regs for work areas, access control, camera/security monitoring.
I don't think I agree with those labor numbers when considering all extras aside from growing. Harvest. Planting. Equipment maintenance. Post. Delivery. Sales. All on top of maintaining spaces and actually growing. Are 1-2 people working 24/7/365. Vacations, sick, family emergency. Plants still need tending.
Lots to consider, should be a fun project. Good luck.