There's no absolute answer here, but you probably want to keep the paths as short as possible
So use as many vias as you can fit, perhaps joining them into small groups with top layer planes (but don't forget the thermal relief to make it solderable...)
I would run a (fairly wide) trace parallel to the ground pins, then use thin traces to connect those pins to the ground trace.
The reason for this is so that those pins solder correctly.
The wider trace can connect to whichever layer you desire with one or more vias.
If I would run this amount of Amps over my PCB I would need a 110mm
wide track to carry all the load. The complete location for it on my
PCB is only around 100mm. Can I just use 2 planes to connect
everything together or should I worry about a short circuit?
If you were to locate all the supplies in the same place and fan out all the LED's from the ...