1: Is the first town center the most important town center?
The first TC seems to be the only one that blocks enemies to build near your colony.

[(2):Units that get a stat boost from the TC trough various ways:
Haiti units and French foreign legionarre are units which get stronger the further they get from "an"* TC, while the Ethiopians have a unit which gets stronger the closer it gets.]

2:Is the first TC that gives this bonuses?
If yes: Does the destruction of the Main TC make the units above useless (Average for Haiti)?
Does that mean the civs like Haiti have to Protect their TC like a king in an regicide game?
Does that make the canadians the worst ally for Civs like Haiti since they have a shipment that gives 2 TC caravans at the cost of Reduced HP for all TC's?

If no: Which TC has the priority over who's giving the bonus? (For example, 3 TC's at 3 different distances, the further or the closest gives the bonus?)

3:Is this bonus acually tied to the spawn location of the player instead of the TC itself?

4:Why the Latin American Town halls seems to have a limit oh how far it can be build from "an" TC?
Does that mean the distruction of the TC will make this building unable to be obtained?

All Town Centers provide that aura. That's why the Haitian ability becomes so strong lategame.