I would suggest you wire the data lines as a combo of option#1 and #2.
Send data out from a central point AND bring the end of run “returns” to that same point.
That gives you the possibility of doing any of the options now or in the future.
Before anyone complains about data runs being too long or too complicated, let me suggest you look seriously at any of the simple rs485 boards out there (especially based on the MAX485 chip).
Using these boards on the data lines eliminates any dropped bits due to over length wires.
Max data length using these devices is easily 500m or more and they’re well rated (2Mbps or more) for the data speeds involved.
Wiring is very simple, I often use 22/4 wiring (commonly called “Station-Z” or alarm wire) for the data lines as that gives me 2 power wires and the A/B data wires needed for the RS485 sender and receiver.
I use small buck converters for power injection along the strip in conjunction with a smaller 18AWG “power bus” running higher voltage (usually 24V). The higher voltage is dropped by the converter at the point of usage, that way there are no power drop issues. Stranded 2C18AWG wire is available in smaller diameter versions (approx 3.8 mm dia.) that makes for easy installation that “hides” reasonably well. In your example, one converter at the center of each post strip would likely be enough.
Works well for me on a number of strips from 75 Led’s to more than 600.
I would suggest you consider burying PVC conduit (at least 12mm, perhaps 18mm?) for the underground portions. That can make your life sooo much simpler when things go wrong in the future.
Just my $.02