Detailed response, good info, but yes...a tad long-winded, lol.

$300.00 for nutrients...?
Wow. It would take me over 3 years to spend that much on necessary nutrients. Perhaps 2 1/2 years if I include the molasses and phDown. (and I'm caretaking for 4 of us)

Air circulation and light penetration should be considered when determining spacing, but necessary space is strain and technique-specific. If you don't top, or only top once, you can possibly get-by with (5 gallon) pot edges touching. If you top 'em twice, or train 'em out (twisty tie training) you'll need more space between pots. Also, keep in mind having to reach over plants to water the ones in the back row. not a big deal when small, but get's more difficult as they get taller. Allowing more space between pots lets you slide 'em around out of the way.