"He who marches out of step hears another drum." ~ Ken Kesey
I agree with Shane. If you can set up two rows back to back it will make life a lot easier for thread changes & machine maintenance. Two long rows will also make it easier to see everything that is running without having to walk around the entire shop too much.
I was thinking along these lines. The back wall can be used to hold thread cones on racks. You can walk between each machine and add / change threads without having to constantly walk all around the shop. If room size permits I would add a long row of tables on the back wall as well.