Does this mean once I build my first fortified manor that I will lose all tax revenue and control of any other villages?
No. The villages taxes will be fine. You will loose control on all their manors outside villages
Or is it if I try and build an additional fortified manor from a building near a village when I have already built a fortified manor somewhere else it will then cause tax income not to work for the new fortified manor I tried to build? Does it break income in just the one location or everywhere else?
You can build only one fortified manor near your first village. All other manors near your other villages can't be fortified
If I build a fortified manor and then dont try and build another somewhere else
This is a correct way. Build one fortified manor and not build any other manors - waste the money. You will get abt 8000 profit from fortified manor goods, and taxes from all your villages.