>We had thought of having ALL the AP's from each site in a single Network, but heard against this?
I have done this once for a company for their guest WiFi, because they wanted to see the analytics reported in a particular way. It worked fine, but it would normally be my last choice.
Others have mentioned templates, so I'll let you consider their advice.
I have had a company that had a network they dedicated to storing the settings in (it didn't contain any devices). They got me to write a script that would copy WiFi settings from that network to every other network based on a tag (for example, copy network "default-settings" to all networks with the tag "store").
This made it easy for them to test (copy the settings to networks with the tag "test") before doing a full production roll out.