Today I completed the left half of my split keyboard!
I had a bit of a problem with the LED model I was going to use, since I was planning to sue the SK6812MINI-e, but discovered that it actually needs 5V to work, which is bad since we only have 3.7V coming from a 1S LiPo Battery. So, I switched to its 3mA counterpart “SK6803MINI-E” which can operate at 3.4V instead of 5. Routing wasn’t that much of a problem, a few vias usually fixed the problem.

I still don’t know about the battery pads, I feel like they shouldn’t go where they are (maybe they are too close to the edge?).
But apart from that, everything is ok! Now I just have to make the right side of the keyboard