In a nutshell - a MAX485 IC configured as a Transmitter (Tx) takes a standard digital 5V input (but works reasonably well with 3.3v) and transforms that to a “differential signal” across two wires A&B. You hook those two wires (I add ground as well) to a Receiver (Rx) at some distance (10m-750m) away and the differential is converted back to digital 5V output. The units are small and consume very little power, the majority is the bus termination resistors that consume about 85ma. So your diagram is essentially correct the MAX485 you show is the Tx unit, you just need to add the Rx unit at the strip receiving end. You still wire your strips in order as if there was nothing between them, you just take the output end of the strip and add a TX with a bunch of wire till it reaches the Rx hooked to the next strip’s input.
You need a Tx-Rx pair for every “long” data line you want.
For voltage conversion, you’re much better off to with some of the modular Buck converters to bring things down to what you need. the 78XX/79XX series regulators are effectively just big resistors that will waste most of the dropped voltage into heat. Buck converters are mini switching supplies that are quite efficient. Most you buy now are in the 90-95% efficient range. You pick one that will supply the current you need at the output voltage you want, 5V 5A or 5V 10A are quite common. I wouldn’t trust the one you listed much beyond 2A although they’re small enough to “embed” in a piece of heatshrink tubing, you end up using more of them. For more power I’d try :AliExpress
For an example of an RS485 board off the shelf, try: Aliexpress
Or you can go the DIY route like I did:
That’s a SOIC to DIP adapter board with the 120R termination resistor soldered on.
That scale is in mm BTW.
I package that in heat shrink with a chunk of CAT5 cable and create my “black box”.
Note the label: “Tx120” letting me know the guts are configured as a transmitter with 120 Ohm termination. The orange and white wires are power, blue and white are differential A&B and the green is data input.