Okay, not so newbie but help please?

[Niwashi]

I have to buy a chocobo licence to progress the storyline.

Though I certainly recommend getting a chocobo as soon as you can, since getting around is easier with a mount, i't not needed in order to progress the storyline. My Little Chocobo is a sidequest, not a Main Scenario Quest. You do have to have gotten far enough in the MSQ line to join a GC before you can take the sidequest, but the main scenario itself continues with Slyph-management, regardless of whether you complete My Little Chocobo or not.

I don't have enough of the Grand Company Seals (GCS) - having spent what I had on Ventures.

After gettting your chocobo (which should be pretty quick with the newly lowered cost), I'd recommend prioritizing GC promotions as well. They cost quite a few seals, but unlock more things you can buy from the GC.

1) What's the best/cheapest/quickest way of getting venture tokens?

There's quite a few leves that can reward venture tokens (though not always). Once you advance a bit further and unlock beast tribe quests, they're a more reliable source.

2) How do I earn these GCS in the quickest/easiest possible fashion?

Roulette will give you a bunch once a day.
Do your GC hunting log. (Your hunting log has separate sections for each class, and for your GC. Only the GC section rewards seals.)
If you play crafting or gathering classes, do the GC supply/provision missions. They give both good XP and GC seals.
FATEs are a good source of seals.
GC leves are another.