Trying to work out where your ancestors were before the census proper began in 1841 has always been a difficult process. You would normally have to rely on christening locations and notes and any wills.
The East Sussex Land Tax 1785 and its sister book the West Sussex Land Tax 1785 list all the occupiers and owners of dwellings and lands in each town and village in East Sussex. You will also be told how much the rental for the property is which will give you an idea of the size of it. Sometimes you will also be given extra pieces of information such as the name of the property which will help you to validate your finding.
A book well worth hunting around for, you can find it on Amazon and Ebay and the Sussex Record Society might still sell them as well.