I always try to keep it at 3 ladies or less. Around 3 or 4 they can start to smell each other's natural vaginal fragrances, and you have to really step up your game. That shit gets everywhere and they smell it like wolves.
You have to expect they'll find out, and plan for the worst. It's around 3 simultaneous bitches that I start to plan out a murder, and if I get up to 4 you will know that I've already got multiple aliases, cash and ID's/licenses, video with changeable time stamps showing me all around town at the ready, alibis everywhere, and plenty of duck tape and black trash bags.
Most of the time it ends up alright, but you have to be prepared for shit to go wrong quick.