Wow, I wasn't expecting all of that. But very insightful.
If the wireless solution supports VoIP phones and APs, then everything else simply and literally falls right into place. I just recall back when VoIP and WiFi were both emerging (roughly ~2007), that the two technologies just didn't work all that well, and especially together with VoIP over WiFi with their specific needs, with jitter and lost packets. If the wireless won't or can't work like this, then the last standing option would default to fiber, with a boat load of more option and related questions.
All the buildings are adjoining, well under 200 feet apart, and on the same block, so the power ideally should also be sourced from the same sub-station, and well grounded (electrically). The driveway/parking lot allows for 2 (doubt 3) utility/service or box vans (Sprinter 3500, F550/5500 Cab & Chassis, etc.) in series, or ~5 in parallel (guessing).
The main building (under 200 feet long), some claim the ~150 foot CAT5 LAN cable for the back computer, and a straight run, just barely makes connectivity, but it also runs along the central load I-beam in close proximity to the various high voltage power lines (for a welder +/- plasma cutter, etc.) and I imagine that the CAT5 LAN cable is not shielded either.
Using an existing conduit or burial of a new conduit would be nice, BUT it would definitely destroy the driveway/parking lot for a very long weekend (asphault or not, still rough) given all the unknowns. It would, however, offer the opportunity to centralize the air supply between the buildings with the option for parallel or fail-over redundant systems.
The Unknowns:
Is a 1/2" conduit big enough for pre-terminated fiber or is it a limiation? (potential cable sources from discount-low-voltage.com or fs.com)
- a video from discount-low-voltage states a minimum 1.0" conduit for their sleeved and pre-terminated fiber ready to pull solution
Are the locations or path of the ('ducted') conduits below ground known?
Does the existing conduit have sweeping bends or harsh/tight bends? how deep does it go or the over all conduit length?
Are the conduits simply for egress using direct bury cables?
or Are the conduits "ducted", that is open end to end with no obstructions, corrosion, or otherwise collapsed?
Do we know where all the utilities and services are located (water, sewer, gas, storm drains, etc.)?