Network Structure

Which network levels (production network, office network, Internet, etc.) should be established or respected?
Which zone concepts (i.e. DMZ, island network) are to be used?
Which technology for workstation clients should be used (web clients, fat clients, thin clients, virtual desktops, etc.)?
Which hardware and network redundancy is needed?
Is additional hardware required in order to ensure data security?
Which cross-system data flows and data flow directions are expected? What is the leading system?
What actions should be taken into account to bridge larger distances between subnets or individual systems?
Are there any requirements or known restrictions on bandwidth and latency?
Are interfaces to other systems outside the ISA functions (i.e. weather information from the Internet) required?