Spot on, at least up until "7, 8 and 9 are unit that make up a whole". The "whole" here is what was already mentioned as the "Lindblum made thing" (which in fact is not so much a thing as a collection of things). I'm not sure what you mean in your second paragraph, but the second half of the riddle really just tells a story that gives you directions to the answers. Let me rearrange it for you, see if it clears things up:
The nimrod arrived in our creator's home
Then headed linearly forth four times, and found us there.
Also of note is that the nimrod is not an specific entity in the game, it's just a hunter in general.
Repost:
Come to us, in times of leisure
Don't be blinded by the treasure
Maximising your potential
thrice from seven, quite sequential.
Found by the nimrod that arrived
In home of minds which us contrived
then headed linearly forth
four times, though still far from the north.
Wrong guesses:
Any/all of the Coffees
Any/all of the Zodiac coins
Any/all of the Tetra Master cards
Terra Guardians
The mirrors in Ipsen's Castle
The 'Aloha' equipment
Mognet
Chocobo Air Garden
The Treno shop monsters
Chocobo Hot&Cold
Daguerreo
Fossil Roo
Kuppo
Feeding Moguta
Hidden item around Oeilvert
Mognet Central
Tantalus
Chocobos
Festival of the Hunt
Frog catching game
Jump rope game
Chocograph pieces
Card Phantoms
Genomes
Black Mages
Hilda Garde III
Exploda
The Jewels
Ozma
Statues in Lindblum
The Royal equipment of Lindblum
Hints:
The answers are related to Tetra Master and Cid.
That relation will be obvious the second you hear the answer.
The answers are not related to the main plot.
The part about the nimrod relates to Lindblum.
The answers are not abstract in any way.
"Thrice from seven, quite sequential" means 7, 8, 9.
The answers were made in Lindblum, where their maker is also from.
The answers are not living things.