I agree with the idea of picking a room where they can play. In our house in Washington, We had the children sleeping in one room. Then we were able to use the third bedreeom for a playroom. We started with their toys in bins on two 6 foot bookshelves in the playroom. If the toys started to overload the bookshelf I would sort and get rid of toys they no longer played with (outgrew). Eventually, the two bookshelves were moved to the Laundry room, and the children were allowed to get no more than two bins out at a time. Occasionally, they would bring those 2 bins to the living room, but for the most part they played in the toyroom. They were reauired to clean up before getting any more bins out.
Here, we have too many children to put them all in one room and have a toy room. However, we have a huge linen closet. We use half of the shelves for toys, games and puzzles; the other half for linens. We have a cedar trunk/coffee table for blankets. We have a split living room, so the front one is a library/school/toy room. The rule still stands that they are allowed no more than two bins at a time, and they must clean up before changing toy sets. A couple times a year either I or they go through the toys and decide what we can give to other children who have no toys. One of those times is right before or after Christmas. No new toys come out till they have a place to be put away.
I do the same for coloring papers. Each of the older children have their own bin; that is where they can keep their papers. When it is full they must decide what to keep and what they can let go of. For the younger ones and pictures drawn for me, I have a file in my desk. I plan to get a corkboard so that I can hang and rotate the pictures in my file.
For business I have our desk and a two drawer file cabinet. They are in the living room, so that helps motivate to keep them organized, however, on the days when I just can't get to them, my desk closes up to hide the mess. I am a neat (organization) nut, but not everyone in our family is. The desk with a door was a compromise that keeps us both from going crazy. For a smaller house that is full of children, we are able to keep it fairly neat using these methods. Also, we have periodic pick up times during the day. I will tell the children that it is time to pick up excess toys and put them away. You could make this time a game, and offer a reward to the one that picks up and puts away the most toys (in their correct spot).