On that scale, feeding with liquid nutes is going to be very expensive and labor intensive. It seems like you're approaching this as though it was an indoor grow and just scaling up, which is a big mistake, IMO. Outdoor is a different animal altogether.
The way you do big plants outside is with a well-amended mix, lots of benes, topdressings and teas. The micro herd and nature's synergistic processes are yours to harness, even in the G-pad.
You should look into Tom Hill's large plant soil mix. Super cheap, and proven to produce. Id post the link to the IC thread, but that's probably a breach of the TOU. Tons and tons and tons of useful information in those 300+ pages.
I think coco makes a fantastic base to a rich soilless mix, just don't skip on the amendments. If I were you, I'd look into some or all of the following:
Cottonseed Meal and/or Soybean Meal
Alfalfa Meal
Kelp Meal
Neem Seed Meal
Crab/Shrimp Meal
Oyster Shell lime (powdered)
Gypsum
Azomite
Greensand
Humates
Chicken Manure
High P Guano
Soft Rock Phosphate
Vermicompost (EWC)
Nice black organic compost
And about 30% perlite/pumice/scoria. I actually prefer pumice and scoria because they stay down in the root zone rather than floating up to the surface as perlite tends to do.
You're looking at a purchase of about 20 yards of mix - why not consult your local bulk suppliers of soil, compost, vermicompost, etc. about making a custom mix for you. I would bet that you'll find the cost difference negligible. Depending on what kind of materials and mixes they have available, you could drop ship your amendments to the soil company and then have them mix and deliver your medium.
If it's too late to do it this year, make sure you at least explore the option next spring.
It's pretty wonderful to see AAA results simply feeding plain water and foliars (Calcium25 and brix mix are amazing) in veg, and the occasional tea or topdressing in flower.
Generous amounts of myco applied to the root zone at transplant increases my growth rate 2-3x.
Hortonova applied correctly during veg and stretch will completely take care of your support/staking issues.
1/2" drip emitter line is your friend. As are irrigation injectors.
I hope this little rant has been helpful. If you're really going to go for it, you should spend a couple days reading through the growing large plants outdoors thread over on IC.
Don't forget to keep us updated about how things unfold. Good luck!