Looks like you’ve got a handle of stuff pretty well!
Your power injection calculations for 60/m will be better than 1 inch, so if you use their 1inch setting it just ends up being conservative for you. @wizard might know the equivalent wire gauge to use when considering most common strips (how much copper is in a flex trace?)
My rule of thumb has always been to inject 5V 60/m strips every 4 meters (every 240 pixels).
Correct on the power supply - with a single power supply, you can keep the positive lines connected through the run and inject power whoever you need.
Actually there’s a few different individually addressable chipsets that use 12V for the LEDs. Then you need to provide the Pixelblaze with about 300mA of 5V via a separate power supply or buck converter.
I’ve recently been a big fan of the GS8208. WS2811s are cheap and come in a lot form factors like strings/strands. WS2815s are also popular for strips.
All the 12V WS2811 I’ve seen use a small external IC. This can be on a small board soldered to a through-hole LED to create a “bullet”, on a small
PCB to make a puck/module, or surface mounted on a flex strip. My only experience with them has been when I want a non-strip 12V form factor, but now people are manufacturing GS8208 (actually an 8206 external IC) bullets as well. The brightness curve is so much better, I’m probably never going back.
Like you noted, the WS2815 and GS8208s both have a backup data path that the 2811 does not. I guess it’s kinda hard to know how often that has ever saved the day.
For the best looking patterns where you can definitely see the difference, there’s still no beating the 5V SK9822a on an engine that can handle it, like Pixelblaze. Better gamma, more reliable long runs, faster data and frame rates.