You should only need about 100m of drain pipe, or a little over 300ft, whether drain pipe or PVC. Here, the drainage pipe is .82 per foot, and PVC is 1.24 per foot.
Those bends would probably work; my minor concerns would be whether they stay in place without wobbling around, and having enough roots to make it through the bend, and into the column. Minor concerns, like I say.
If you get tired of paying for neoprene pucks, you could try using foam tube pipe insulation, and cutting it down to the thickness you want. I make mine about an inch thick to support the stems better. A 6 foot long piece is less than $3, and will give you 72, 1 inch thick pucks... Just another DIY option.
For tees and feed/return lines, I'd go with at least 1 inch, but try to stay under 4, depending on fitting prices. Even 1 inch tees are like a buck a piece, before bulk discount, but it may cost more after considering reducer fittings to get from 4 inch down to 1. With the silo diameter, you may be able to connect all the columns at the bottom with 4 inch tees, but I don't know if you can get little 1ft rounded pieces to connect the tees or not. You'd probably need the 22.5* elbows too. Tees and elbows are 5-6$ each, before discount here.
I think you're right about needing indica dominant hybrids, and the hardest part will probably just be finding 4 true 8 week finishers. A lot of stuff people usually take at 8 are really done more like 9 or 10, but people want to keep that 8 week schedule.
I've heard good things about AN and Floraflex, but haven't used either. I have heard AN is pretty expensive though. Regardless, if they're liquid when you get them, you're probably over paying for the water weight. You might want to consider a powdered nutrient that you mix with water yourself. I mix my solutions 5 gallons at a time, the first gallon or so is hot, to dissolve the nutrient, and the rest is cold.
I'm not sure if you can order Megacrop where you're at, but you should be able to get JR Peters, ("Jack's"), which is said to be comparable in price and performance.
The way I see it regarding RO filters, unless the water is very hard and dangerous, they remove minerals like calcium, that you'll just spend more to add back anyway. Plus, they waste at least as much water as they clean, generally. Just my opinion though.
It sucks that customs is so enthusiastic with their theft, but with enough research, you should be able to avoid most suspicious looking senders and labels. You can avoid over priced hydro stores, and find most things from electronics sites, home supply stores, or Amazon. If you're decent with electronics, you can DIY your LED lights with parts from places like Cutter, Digikey, or Arrow.
That kit is nice looking. I'm sure you could DIY it for less, if you wanted, or you could just get it all as a kit, for convenience sake.
A 600w MH might work alright for veg, but you may want more wattage, or to spread more smaller lights across the area.
For 4 mothers, 2-4ft wide and high, you'll probably want to use at least a 10 x 10ft area. I don't think 1 600w would be ideal to cover the whole area, but could be sufficient for veg if you hung it high.
