Spacing 20" pots

I've got 20"x20" round pots 18" deep and against an 8-foot trellis, of course filled with lovely perfect MM.  They are on a 24'x8' second-story deck.

According to the book, Cukes are 2/sqf.  I think I could force more than that in these round pots, but I'm also looking at trellis space above the pots.  I want 3 pots
per 6' linear space, so 6 pots of 2 cukes each, is 6 cukes on a 6-foot trellis, and that seems to be plenty. Cukes are prolific anyway.

Melons are 1/2sf, so 1 plant in each pot seems reasonable.  Also same trellis problem, 1 vine per 2 linear trellis foot.

Winter Squash is 1 per 2sf, so the pots should be fine, but trellising may be problematic 1 plant per linear sf, depending how vigorous the vines are.

Summer Squash seems most problematic.  1 plant per 2 or 9sf.  A 20" round seems inadequate, except it's only the ground spacing.  And they are bush plants, so no trellis.  Pots can be spaced out further as the plants grow.

The varieties are:
Summer Squash, Bush, White, Scallop
Summer Squash, Zuch., 49ers Golden
Summer Squash, Zuch., Grey Summer
Summer Squash, Zuch., Golden
Summer Squash, Zuch., Greyzini
Summer Squash, Zuch., Black Beauty
Winter Squash, Delicata
Winter Sqiash, Table Queen
Winter Squash, Walthum Butternut
Watermelon, Sugar Baby
Melon, Early Silver Line
Pumpkin, Small Sugar
Cuke, Early Spring Burpless
Cuke, Lemon
Cuke, Mandarin

Any thoughts on spacing?  (Or varieties?  Or big veggies/fruits 2 stories up?)

ENT, I kind of push the envelope on vining plants so don't take my word alone.  I have summer squashes one per 12" pot.  2 cantaloupe in a 12" x 12" x 12" box, winter squash at 1 per square (1 linear foot), etc.  What I would do is line the pots up next to each other or as you have planned, alternate tall thick vining winter squash, low fall-over summer squash and tall med-thick vining cucumber.  Let the summer squash fall towards the deck, the thee others up the trellis.  Prune dead leaves or supporting leaves as the fruit is picked to allow sunshine and air circulation.  I am so jealous of your plans / problems!   

My only concern is whether the deck can support the weight of wet MM and fruit.  I can't wait to see what others suggest!