Keep in mind that working fires will almost always be assigned an Incident tg in the systems that use the Incident talkgroup structure. Each Incident group has several associated tgs. Most of the time, all operations use the main tg, e.g Incident 20, but if a staging or water supply officer is designated, they may use their own tg that is related, e.g. Incident 21, Incident 22, etc. The Announce 20 tg would be heard on all Incident 2x tgs. Incident tgs can be assigned on a first come, first served basis, or they may be assigned on a battalion or regional basis - depends on the jurisdiction. Ops tgs are typically used for local alarms, minor traffic accidents, etc., and can be regionalized. Many Maryland counties use the Incident tg structure in some form, but may not use the Incident labels.
Specific notes:
AACo is divided into 2 regions (North / South) and they tend to use every tg in Zone 1. It's a very busy system, so I would program them all (except maybe 1N, which is the administration tg.) Also, the G5 doesn't do SmartZone.