Hi Wendy,
I wanted to add that some of the local libraries would hold more records at times that far back in the form of maps of the townlands and who lived on them. They should be readily available if you are going to be visiting Ireland during normal business hours and by appointment if you want to get maps etc.
I find that a lot of the records for that time frame are available in the forms of some church records and a lot more in the forms of wills, deeds and family papers you can find at different archives, including PRONI where a lot of records are housed that were not burned or lost in Dublin's 1922 fires. It is worth a search at
www.proni.gov.co.uk in the family history section to see if any records may be there. I see there are referenced a few but they are a bit later than what you are wanting, but it may be a relative to your Wheatley/ The one I found was a dissenting minister? Do you know if your Thomas was related to John Wheatley? There also seems to be quite a bit of research done in USA family histories on the New England branch of the Wheatley's. Have you seen this research and does it connect with yours?
On a side note: Wicklow borders Dublin, so when researching, include Dublin in your searches.
Please do keep us posted! It's always exciting to see prefamine research! It can be very rewarding.
Ginger