Hi Kerry:
Depending on how much time you want to spend on the Crosthwaits; there are two sets of additional records (quite valuable in my opinion but sadly underutilized in American genealogy) that are available from the comfort of your home.
One is land records. The general index for Albemarle County Deeds is available from Familysearch; the index entries for Shelton Crosthwaite are here: https://www.familysearch.org/ark:/61903/3:1:3Q9M-CS4X-P3B6-C?i=71. It appears he bought a total of 400 acres of land in 1799/1800 and then sold 388 acres in 1803 and 400 acres in 1809. I have only looked up the last deed, from 1809 (right-hand side here); this shows that when he sold his Albemarle County land in 1809 he had a wife Elisabeth and was living in Nelson County, VA (adjoins Albemarle County to the SW).
As for Nelson County, the general index is accessible only at a FHC, but the individual volumes are also indexed and can be accessed from home - here is the index page to vol. 1 of the deeds that shows both a purchase (very first entry under C) and several sales (around p. 100) by a Crosthwaite. I have not looked at these individual deeds.
As for Rutherford County, TN, if you look at the Deeds index, right-hand side (which is the Reverse Index, or index of purchases), you will see there are purchases listed for Shelton in vol. G, p. 304, and (on the next page) vol. I, pp. 219 and 240. Unfortunately, those are the two volumes of deeds that have not been filmed (see https://www.familysearch.org/search/catalog/358486).
Incidentally, if you go through the Albemarle Co. general index, you will see that there is no entry for Thomas or his siblings - so they did not have any of their father's land to sell when they left for Tennessee. There also appears to be no purchase by Thomas in Rutherford County, TN.
The other set of records are tax lists. Albemarle County personal property tax lists (a poll tax on each white male age 16+ plus a tax on slaves and certain animals) are online. There are two tax lists for each year (two collectors for separate parts of the county). In the two years I looked, I have found Shelton in 1800 (left-hand side, third name from top) and 1801 (left-hand side, 5th name under C), but have not found Thomas or his siblings. If Thomas's son William was really born in Virginia in 1805, one would expect Thomas to show up in one of these tax lists.
For Rutherford County, TN, there are tax lists available for 1809-1813. Looking at the 1812 tax list I found Thomas (right-hand side, about halfway down), taxed on 1 poll (i.e., white male over 16) and 1 slave but no land, as well as Shelton (left-hand side, 9th entry from top) taxed on 1 poll, 19 slaves, and 812 acres of land.
