Rachtubimenoz

Hi folks, I'm pretty sure that it has been asked there is no knowing how many times but so far I couldn't have found a detailed explanation so here I am. I want to create B team leagues which mimic the first 3 or 4 domestic divisions (like if the main team relegates, they relegate, too), U21 leagues which have best academies & U19 youth (regional) leagues without promotion & relegation, U21 & U19 super cups and want to know if these cup finals sending the winner to UEFA Youth League. I don't want anything but direction and details; like what I should delete or create first, where I should add the competitions, how I edit advanced rules etc. because so far I've failed whatever I tried to build a structure for that. I found some videos and explanations on several platforms but they don't have the content I want to create and whenever I try something, there is a bug or confliction. There are some custom databases but either their authors have cleared the database changes or they've done it randomly. If anyone could help me about that, I'd appreciate it.