I took a quick look at parts of the video. The concept works,
I've done it for small areas where there is a problem and
no natural gravity drain solution.

You said there is some kind of existing drain that may
not be working correctly. Is this private? Public?
Starting there might be a better idea. Even if it's private,
maybe you can chip in with someone else to fix it, improve it,
etc.

As others have said, better check on ordinances regarding
pumping the water to the street. Also, does this proposed
sump pump have to only work when it's not freezing?

Retaining wall, that's a lot of concrete and a huge job,
100 bags to mix by hand. IDK how much looks matter, but
there are retaining wall block products that would look
better, but probably cost more.