Greetings,
I think I understand that you are trying to create a single .MXD template which each user can work from for their individual county/project and this will allow the cartography to be identical across the board; however each county's data is in individual files.
An idea of how I would go about this is to simply pull all of the data in to the MXD, then group the files by county in the table of contents (shift+click to select the files in the table of contents then rightclick and select "group", then rename the groups to match the specific county). Meaning Group 1 = County A's Streets, parcels, boundaries etc; Group 2 = County' B's Streets, parcels, boundaries ets.
I would then let each user either simply turn off or remove the county groups which do not apply to them. This way all you are doing is setting up a single template (not 10) and they can simply turn on and off what they need to use.
As far as symbology, set up one county's cartography how you want it, then save each file's symbology as a layerfile. Use those layerfiles for each county's data via the Layerproperties>Symboloby>Import button.
Hope this helps!