I am in a Volunteer ambulance service we are also a USA Medical Corps member so we have a response to MCI's and natural disaster events. We mainly work sporting events, fairs, festivals and so on. Some are loud (Cage fights, heavy metal concerts etc) so voice comms are not very useful. Some are spread across hundreds of miles vast sections lack even cell service (like the Fireweed 400; Sheep Mountain to Valdez, AK). And some we run a field clinic with 3 exam rooms and 5+ roaming teams of medics and 2 fast response team in a non-motorized setting with a tight HIPAA compliant comm net. So our needs are quite varied. Several of us in leadership are IT or comm pros (our comm director owns a industrial communications sales/service for oil and gas exploration companies) and have gone though a number of potential solutions. This is what we do: Our backbone for disaster work is the ALMR radio system some of which can carry data or will soon. We have a few SAT phones for bush work. Over that we have our own VHF/UFH simplex/duplex radios with repeaters and FCC assigned channels (however that works) for our day to day work cupeled with regular data plans with a ATT MiFi type divice for PCR's, SCAT forms and as much paperwork as we con do electronically.
I have to wonder why you need the local networking?
I know I didn't address the question of the best way to set up an EMS/Fire network, but that's what I got. Good luck.