I am the hinge of a MFM V, and we cohabitate with my 17 year old homeschooled daughter and my adult son, who is 25 and is disabled.
At first I was splitting my time between two households, but we did the move-in thing over the course of a few months. My boyfriend PunkRockAwesomesauce integrated into our days with overnight visits, then multi-day hangouts and eventually weeks. It was planned out - we had to prepare space for him to become a permanent resident. We had several discussions about how our household would function.
Everyone has their own bedroom - in the beginning, my husband DarkKnight and PunkRock had twin bedrooms - they were the same size and layout on the same floor of the house, and they shared a bathroom. I have the master suite, with my own bedroom. They took turns sleeping in my room with me, every other night, each having a drawer in my vanity to keep their toiletries in. They have their own color towel and toothbrush, so there are no mixups.
Recently, however, PunkRock has moved down to the basement, where he has his own bathroom, bedroom and huge living room area, which my son was previously renting from us. (My son is now upstairs in PunkRock's old room.) PunkRock moved for a couple of different reasons, none having to do with poly or equality or someone being unhappy or anything like that.
That said, both of guys always had an additional private space to retreat to if they didn't want to hole up in their bedroom and be alone - DarkKnight has a separate office in the basement, and PunkRock had a corner of the basement living room as his painting area, with a desk and a space for all of his materials. We liked that they had the ability to go be away from each other, if needed.
I think private space is important in a poly set-up. I am a total extrovert, so I don't mind sharing, but my guys are introverts and need space that they can close off the world, when needed.
As far as finances go, we have a joint checking shared between the 3 of us, which I use to pay the shared bills from, and they each have a private checking and savings, which they have their wages direct-deposited into and can use however they wish. This is great because it leaves them their autonomy, and they can still surprise me with presents.