I came across all of these issues and many more trying to make a good light color scheme for my systems. Two interesting findings I did not see discussed:

1. It makes sense in retrospect, but I was very surprised at how much more subtle light themes are compared to dark when viewed on different screens; of course their hardware and software configs lead to variations on the color output, but light dominant changes are perceived so much more drastically than dark ones. This is a serious issue if you will be porting your theme to computers with a variety of screens and configurations.

2. Occasionally, you need to drop to a linux or bsd console with very limited support for fonts and fancy colors. Then your `fd` and `exa/lsd/whatever` may be unusable and annoying, especially if you have mapped the latter to `ls`. I managed, after a long struggle, to get a working fbterm in my system to get decent terminal features without X, but fbterm has its own issues. You need to account for this use-case, especially when configuring vim colorschemes: make sure that you have a fallback theme for a feature-poor console or you have really practiced typing vim commands blind :D

Edit: here is a screenshot of my stylized fbterm screen, obviously not for serious work, but meant to demonstrate what you can do without X: https://i.imgur.com/RbDRgtD.png