OK, so I have a partial but very usable and clean answer to point #3 by @owynter.
However, all this config change makes me think that we lose the consistency and universality of Tailwind, especially when sharing components between sites or users.
So, what about the ability to specify fallback standard values that could be used if the custom CSS variables don’t exist on the target site?
For instance, I paste my HTML here on the forum, someone gets it and pastes it in his own site but, as he doesn’t have my config variables, the fallback values are used.
Another nifty trick is used in Figma to code plugin, with ROUNDS custom values to standard Tailwind values when exporting.
The reverse mechanism would be awesome when pasting into Cwicly 
Cwicly would round the standard values to your closest custom values, et voilà!!!
SOrry, these are only thoughts… Just exploring to check if TW fits my needs.