Sound’s like you’re looking at something like a CAN.
Within a building and between fixed points (for data access) I’d probably recommend some kind of wired solution, but you have to be little careful to ensure that the segments of cable are no longer than the maximum recommended for the technology (think it’s around 150m for standard Ethernet), and that sometimes interference can be a problem in factory settings. (Fibre-optic networks are more resistant to interference, and think the cable runs can be greater)
They’re also much easier to secure, as a digital intruder either requires physical access, or gets in through the "Internet".
It would need a little planning as to where the data can be accessed, but that’s probably already been figured out, as part of the buildings design. Also remember in factory ascetics should really take 2n’d place to productivity.
The systems in place for assembly/stock management dictate where terminals are required for those departments, but I’d recommend having some fixed terminals (with printers) near the goods bays to direct the forklift drivers to drop/collect goods at the correct location. It’s difficult to beat old fashioned paper, especially when using forklifts, handhelds have a tendency to get dropped and smashed.
Maybe have a few portable devices for those supervising the forklift drivers. (perhaps running more like blue-tooth enabled peripherals than full machines)
Between the building really depends on how far they are away from each other, and how much data needs to flow between them. If the building are some distance away from each other, but when it’s still feasible to lay a cable, I’d seriously consider a fibre optic link, even if the rest of the system doesn’t use optic fibre. If the buildings are in line-of sign then laser/microwave line of sight communication links could be an answer. Otherwise you’ll need to use a leased line (as do most businesses)
To figure out what’s best, you really need to do a cost comparison of the different methods, consider cost of installation, and running costs. The optimum solution is difficult to find, but should be one which has some degree of future proofing.