1. What size are the 90 degree Barbs? Are they the kind of Barbs that would connect in the Fuel system of a Car or something different?
1/2inch. They can be found in the sprinkler dept. at hardware store
2. What size is the Drain Pump in the bottom of the controller?
300gph pump will do the trick, but little bigger or smaller will work
3. Do I put a 3.5 Gallon Bucket inside of a 5 Gallon Bucket? What's the purpose of doing this?
Or you can use (2) 2 gallon buckets. The top bucket holds the plant and the medium. The bottom bucket is for draining. The bigger buckets are good for bigger plants
4. I can't find the Float Switches you've used and the website is not coming up. Do I use pretty much any Horizontal Float Switch and if I do, how do I turn the float around? I've not found anything that would allow me to take it apart and flip the float over (I may not know what I'm looking at either).
I would just buy one already made. hydroponics(dot)net. You can make it yourself though if you understand how.
5. Would the 50 Gallon Reservoir be overkill for a 6 bucket setup?
50 gallons is a good amount. You could get away with less if you need for just 6. Maybe 30-40 gallons. If need be you could even use less