I start games with loads more than 3 leagues
It depends on your computer but I have 3Ghz computer with 1GB Ram and use all of these leagues
England
Scotland
France
Germany
Spain
Italy
Greece
Turkey
Belgium
Holland
Portugal
Brazil
Argentina
Mexico
USA
South Africa
With Medium Database
If your computer is slower or if you only plan on playing for a couple of seasons with a top team then only use 3 or 4
But if you want a long term game with a smaller team then i think its best to use loads of leagues like this beause if you have fully operating leagues of teams that all have full squads of players and produce large batches of young players then you are going to have more choice of players to buy and there will be better and more youth players that come through the youth teams
I also find that using more leagues gives you Players for countries where you dont have a league
for example you will get more players from Ivory Coast, Ghana, Nigeria etc by selecting south african league and more from Chile, Peru, Colombia etc by using Brazil or Argentina
It doesnt go that slow, Except in the transfer window when there is more going on. if you go on holiday in between your games then its ok, I highly reccommend using a lot of leagues if you can
coz it makes it better in the log run