Adopting a new ferret! How do I get him introduced to my girls without any fights or harm?

My brother just messaged me - his friend has a male ferret (~3 yrs old) and doesn't want it anymore. He will come with a cage, and I am probably picking him up on Saturday. I have two girls (Alice & Piper) and I am just wondering how to properly introduce them so nobody gets territorial or scared or angry?

My ideas: Keep him in his own cage for a few days, and have them out A LOT for supervised play time. Maybe have both of their cages open for exploration purposes, and slowly introduce him to their cage... wash all their bedding before putting him in their cage for good.

PS- Is three ferrets too many for a double story Ferret Nation cage?

Thanks Ladies and Gentlemeeeen!