@Caokrodilo You also have to organise the calendar well because there are a lot of matches. I do something like that, so what I've done is to rework the domestic divisions so that we have a maximum of 30 matches. That leaves a bit of leeway for the secondary leagues. In total, the ideal would be to have around forty matches. Then there are the national and continental cups. You could quickly end up with more than 60 matches.
As @themodelcitizen said, there's also the whole Pro/Real system that needs to be set up individually for the secondary leagues. It requires patience, but it's a good challenge!
Study the structure of the Brazilian SI championship - it's very interesting. You can also copy and paste the championships that interest you.
Personally, I use different files for each championship and when they work I import them into my main file. That avoids error messages. Basically step by step.