I like Molex, but not for outdoor stuff. It looks like he's using a single Molex for most of the channels. So why not just use the standard water tight three-pin or four pin connectors?
They're inexpensive and readily available. I have 32 of them for my Mega tree (16 for data and power and another 16 for power injection). So I don't have any common conductors. It could be cool to have a large molex for that, but it sits in surface water on concrete and I've never had an issue with GFCI or shorts. Just an option.
Thinking about your question about current draw, with low voltage (5V, 12V) you need to calculate your current draw and ensure the cables/connectors you're using are sized large enough. If so, then the cables are fine. Too small of conductors for the load and you'll wind up with heat, voltage drop and poor performance (like flickering or incorrect colors).
Here's my Mega tree wiring. It's not pretty. It's all 5V too. If I could do it again I would use 1/2 of the connectors simply by using 12V. But it gets the job done, it's not much time to plug in once a year and I've never had water incursion. All 3-pin waterproof connectors that are labeled.
This is a pic of the controllers. Again, I could have cut the number of cables in half if I used 12V, but hey, this is still running today and doing a great job. I would not need power injection with 12V. But this was back when 5V was the shizz nizzle. So not perfect out of the gate, but always learning.
The Holiday Coro box on top of the stack houses my network switch, an E6804 and power supply for the mega tree pixel Bethlehem Star and an E6804 for a pixel cross I put up front and center.
