Couple questions about detail level

I have some questions about simulating leagues in full detail vs not doing so.

1. From what I have heard simulating leagues in full detail makes AI stronger. How does this work exactly?
2. Let's say that I have Germany playable but on no detail. Will this slow development of everyone in Bundesliga?
3. In my main save I currently have International competitions, European competitions, and England simulated to full detail and playable, while having all other leagues (Germany, Portugal, France, Netherland, Italy, Spain) playable but with no detail. Will doing so put England significantly ahead of the rest of the countries?
4. Kind of going along with 3, I am thinking about changing all the countries above to full detail. Will this instantly make the game harder (by making AI stronger) or will it take some time for countries to catch up?

Unless you have a supercomputer it will slow the game down and put pressure on your free memory

I mean it seems to work decently fine for me when I tried it yesterday

Good luck through the season