I'm simply in love with your league! I picked Soljarnes to play because of their colours, but I moved them to Regionsliga 3, since I wanted to play from the bottom.
As a suggestion, I would slightly change some rules. Youth teams should be U18, instead of U21. Instead of 5 non-EU, the league could have a registration rule similar to UCL (25 players, being 8 grown in the country, 4 of which must be grown in the club, and U21 players don't need to be registered). Of course I could do it myself (maybe I will after I try it the way you devised it), but I found it interesting to share this, just in case you like the idea.
In FM 21, I did a custom league structure for Youth, using an independent relegation/promotion system and cups. I like it the way it is already, but I love it when there are more things for Youth teams.
Anyways, when I finish my journey with Soljarnes, I'll definitely come back to tell you! Thanks for your effort into making such a nice custom league!