How many industries can be placed on a 4 x 8-foot layout?

[Ralph S]

What's the best number or what's the maximum number of industries that should be or could be to put on a 4 x 8-foot layout.

This pertains to HO scale modelers.  The reason I ask this is....   I think I've overwhelmed my layout by trying to place too many industries on my new section of 4 x 8 or I may have too much track on that same 4 x 8.  I thought this section would be my industrial park, but again I don't seem to have enough space for both the track and industries that the track should be able to support.   I'd show images of my layout but, after looking through Sheldon's layout, I'm too embarrassed to show my behemoth, and it's nowhere near completion.  So I'm scratching my head, (and my kids are of no help) in how to place all of what I envisioned as an industrial park with rail access.

Everyone's thoughts are welcomed, cause at this juncture, I'm hoping I haven't overspent on buildings, scenery and well, one never has enough track, cause I'm always modifying the track.