Chelsea have regularly bought in 3 new starters - in about 3-4 separate seasons including this current one.
When Mourinho first took over (first time) - they brought in Drogba, Carvalho, Robben, Cech, Ferreira, Tiago, Kezman that summer who all where either first team starters or who played more than 25 games in the league for them - so thats 7 players. they also brought in a couple more who played enough games to factor as well that season.
City similar tend to bring in 2-3 per seaosn starters, think this year they brought in 5, and in 10/11 they brought in about 6/7 that summer - Dzeko, Yaya Toure, Balotelli, Silva, Kolarov, Milner, Boeteng, year before that they brought in about 6 as well
It can be done
Different eras though mate.
I'm not using FFP as an excuse either - it can be done - but just don't expect 7/8 new players to come in and be straight into the starting XI.