No matter how big your pot (and I'm a fan of smart pots myself), you're going to have to root-prune your mother at some point. I keep mine in a 1g and just turn a clone into my new mother whenever she gets too big and root bound and throw her into veg.
I built a an attic room that I accessed via my garage through a ceiling door in a very hot climate and ran it for 4 years. If you insulate properly and have adequate ventilation/AC it'll be fine. If you are running HID, use air from through the roof (I put an extra heater exhaust vent in that...
I like 25% perlite with 75% coir. Almost impossible to overwater. However, overwatering will slow growth. You need to let them almost dry out to the point they are about to wilt and then lift the pot to get an idea of what almost dry feels like so you know when to water.
This may not be a good method. I'm always surprised at how much variation there is in water consumption between plants even when they are in the same room and clones. You should be checking the weight of the pot. That's the only reliable method for coco, IMO.
Are you sure all your clones were from the same mother originally? Are you keeping a mother or cloning from each grow?
Is there an advantage to keeping the same mother versus just keeping one clone every grow as your next mother? I prefer just using an extra clone as my next mother but I'd...
You guys have some strange ideas about organic. Cow manure can be organic. Most composted animal waste is typically a great organic fertilizer. I'm growing 100% organic myself and I use blood and bone meal as fertilizer.
I'm a coco grower but I use GO nutes. I usually flush with 1 tsp vinegar, 1 tsp molasses per gallon if I'm worried about lockout/salts. Also, make sure you are getting 20 percent drainage with each watering to prevent problems.
Wait for 5% amber to harvest unless you have some compelling reason not to (like plant's dying, etc.). You miss out on a lot of bud development when you harvest early. I would never go 3-4 weeks without feeding -- just wasting your time. One week is OK. There no reason you can't stop...
Well water typically sucks, IMO. At least around here. Very hard and smelly. I wouldn't wash my car with the well water around here. If it's a large pond, I would use that before I used well water (from where I live).