you want to manage Brazil national team or in Brazil?
1) it is pointless loading up top tier leagues like the EPL, BBVA when managing in Brazil, you will struggle to sign anyone from there as the Brazil league rep is **** in comparison and have very small wage/transfer budgets
2) the lower leagues of Brazil have some of the best bargains you can find in FM, the difference between tier 3 and the Serie A is miniscule... so load up all playable leagues if you want to manage in Brazil
3) you will be restricted to buying mainly Brazillian players as for the reason mentioned above so loading up more than that is pointless unless you want to start your career in Brazil and go onto the big teams/leagues, however, any league can be loaded up or removed every year...
4) the smaller your database and the less leagues you load will prevent certain players and staff from appearing yes... you would never be able to sign Willian with any team for at least 10yrs playing in Brazil (well until the time he is like 33yrs old or so, you know what I mean)
5) 442/424 tactics dont work well in Brazil, they dont have many good wingers in any of the teams and 90% of the opp play narrow and you will get caught out...
6) playable, view only will only load up most of the first team players only (not all of them either) so playable is the best
I hope that explains a few things regarding managing in Brazil
good luck