You would have to manually add the players to the leagues or they will have the same amount of players as they would if they weren't active.
It will also use the quick match engine so the stats will be different. I would never load any as view only. It's basically the same as not loading the league, bar the league tables. Teams won't get full youth intakes etc.
I assume you manage at the top level so if I were you I would definitely at least have the top flights of the most important European leagues active
@Daveincid explains it well here -