Yes, exactly. That’d be the wiring for one of your five channels. I want to point out the terminology here: Wizzard is suggesting you run the whole thing off one controller, which is split into 5 channels with the pro output expander.
It sounds like your largest channel is 245 pixels. At 50mA max per pixel, you’d need 245 * .05 = 12.5A to run that once channel strip at full intensity. Instead, if solving only for this one channel, you could use the 10A DC-DC converter shown in your diagram, and set the Pixelblaze controller to limit brightness to 10/12.5 = 80% brightness. You’ll barely notice the decrease in maximum intensity. Plus, driving the 144/m strips at full white gets very hot, very fast.
Now, since those 245 LEDs consumed all that current, you’d use additional DC-DC converters (after the 12V coming from the pro expander) to power the other channels.
There’s an onboard regulator on the pro expander which will take your 12V boat power and regulate a lower curent 5V to power the Pixelblaze controller. That 5V isn’t passed to the outputs on the expander though - the 12V input power it. That’s why your diagram, which included the 12V->5V DC-DC converter is correct. If you were using Timster’s suggestion to use 12V WS2815 strips, you wouldn’t use this converter. I agree with him on the choice of converter - I’ve had good weatherproofing experiences with the silver finned ones.
(Apr '23 edit: Now the new Sync feature is a potentially much more elegant solution to this.)
Yes, but if you’d like each of your 5 channels to play a different pattern at the same time, you’ll need to use ZRanger’s “Multisegement” pattern and adapt other pattern code into this Multisegment pattern. If you want 5 separate web pages, one to select independent patterns for each channel, you could use 5 Pixelblaze controllers with no output expander. This is less code to mess with, but harder to coordinate anything across the 5 independent controllers.