For a rule of the thumb on helixes; 1 INT = ~2 Mab (Not an exact number, depends on gear and target).
Most of what you got is correct. Helix is extremely dependent on your INT, because the base damage is so low.
When casting a helix, you should focus on pure damage.
Barring the +15 M.Accu from our merits: There is no target in the game AFAIK that is both Magic resistant AND helix-worthy. So there's little point in making a Helix resistance set. And if you do find such a mob, just use klimaform.
Here is the "Best of the Best" Helix Nuking gear as far as I know; barring augment-able items.
Weapon: Appropriate HQ Staff
Sub: Buguard Strap +1
Ammo: Phantom Tathlum
Head: Scholar's Mortarboard +1
Body: Mahatma Houppelande
Hands: Yigit Gages
Legs: Mahatma Slops
Feet: Yigit Crackows
Neck: Prudence Torque
Ears: Novio & Moldavite
Rings: 5INT Ring x2
Back: Gleeman's Cape
Waist: Argute Belt
There is still room from improvement on that set tho. Namely augmentable pieces (Both regular and Mini-expansion Ones).
From the expansions (Considering what Shantotto's got to offer): The only really interesting piece is the possible "INT +6" Moogle Hat.
From FoV Augments; there's the option of Augmenting your HQ Staves obviously. You can also get some MAB on your rings and the mahatma pieces. Also, you can get extremly lucky and score something above INT+2 from a rune Bow for the ammo.
That about covers it for Helixes