There is a natural hierarchy to Aperture (as far as I've found). At the core is a "PROJECT". This is how I do it, but YMMV ..
A PROJECT should hold all the photos relative to a "session" (think "roll of film").
A FOLDER can hold all objects, but the way I do it is to use the folders as an ordering method where I start at a Year (2008) for the top level folder, underneath that, I have 12 folders (01..12) for the months, and within each month folder, I put the PROJECTS. The PROJECT is named YYYY MM DD - (Event name) in which the series of related shots are stored.
If I was to organize your collection, I would probably have Folders with the customers name, and then the different collection of PROJECTS that related to the photos from a customer visit.
You may also want to look at RELOCATABLE MASTERS for this kind of file keeping.
Also -- to me, an ALBUM is a collection of Aliased or references to pictures that are kept in a PROJECT and are used for either printing or publishing as a temporary body of work. They are not meant for permanent storage or association as much as the PROJECT collection is.
Does this help?