A LAN is like a chain, it is only as good as the weakest link. A LAN will be loaded with 4 times the data it was designed for. Designing with the overload in mind will not help. The more money you save on buying hardware, the more you will spend on installation, repairs, maintenance and software. Heterogeneous networks will work given time and money.
All input devices are like cats.
They will ignore you at times just to remind you who is boss. Software Rules Software is a tool, not salvation. Management will buy software as a salvation. The software you use always looks buggy. It is always easier to blame the software for work problems than pointing out real problems to management.