Ok to make detail brushes you should take the items that are inside a room and make them the detail.
For example lets say you make a room. The walls of the room would be your structure brushes. The molding, desks, columns or what ever other “brushes” you have in the room would be detail. That way the vis would vis the room as a whole and won’t go crazy trying to vis all the little structure brushes that are in your room. Models do not affect vis as they are drawn at game play time. They’re kinda like detail brushes.
Now if you are making a terrain map and you made your terrain brushes all structure then you are going to have a problem. Terrain brushes should be detail with “hidden” caulked walls inside them that are structure.
Might want to read up on a few vis tutorials. Keep in mind that Q3BSP is also used for quake and other ID games so you can check some of those forums to get a better understanding of what vis actually is and does.
One other note, did you stop your map compile when a leak occurs? If you are then you won’t get your bsp.