Cool step by step write up. I like the attention to detail and colored guidelines.
A couple things to add though:
1) Wires under the hood must have protection of some sort. Proper looming is critical for safety.
2) The fuse must be rated for what the wire is rated for, not just any amount between 200 and 300. If the wire is rated for a maximum of 250A, it would make zero sense to put a 300A fuse on it.
I strongly recommend the frame to chassy ground. The stock one is like 12awg. I was amazed at how small it was when I swapped to 1/0. While for some it may not be necessary, many people ground their large sound systems straight to the frame for a nice clean ground so this 4th wire is one that really should be upgraded anyways. So theoretically it should be called "the big 4 upgrade"
Just posting the picture for those who want to direct replace this wire instead of running it to the battery post.
Otherwise, nice job man.