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Does an arc node have to be in range of the spell to be used to channel? Or is it possible to turn a 8 inch spell into a 24 inch spell?

Nope, the node just needs to be in the controlling Warcaster's control area.

Adding too the question can a caster channel through an Arc Node that is in an anti-magic effect such as Orin Midwinter?

Arc Nodes aren't casting the spells. Most anti-magic effects will also block channeling, but I don't think Orin does.

For an Arc Node to be used, it only needs to be in its controllers Control Area.

Then you use the Arc Node as the point of origin for the spell. That means Line of Sight and Range will be drawn from the model with the Arc Node. The spell also originates from the Arc Node as well(in case directionality matters)

The warcaster is still the one who casts the spell, so any restrictions will measure from their location and not the Arc Node.

Only a few bubbles which prevent casting also prevent channeling(and they will explicitly call it out)

Very few abilities actually stop Arc Nodes, and even fewer stop channeling in general.