Browsing around I came up with a population of 100,000 in Texas in 1840. I'm gonna float a WAG that 40,000 of these were slaves, leaving about 60,000 White folks.
Looks like you did a pretty good WAG on the 1840 population.
I was just reading "The Road to Disunion" by William Freehling.
(It's a book about how the South moved towards Secession. Can't say as how I recommend it as it took 3 months to get through the first volume of 550 pages. And am about to start the equivalent sized Volume 2.)
Freehling notes that getting figures on the population in Texas during the Republic days is extremely hard. Particularly regarding number of slaves.
There were the usual record keeping issues of a new country without a lot of money and with a small population scattered across huge distances.
Another problem was that as the Texas Republic was a seperate country, slaves could not be legally re-imported into the United States.
Additionally, if Texas decided to stay a Republic, there were a lot of pressures for abolition. England, for example was talking about making its support conditional upon abolition. And Mexico, iirc, had already declared abolition.
Freehling estimates somewhat fewer slaves and the same white population. And he provides some sources. But he fully admits that nobody really knows. He also wrote his book back in the 1980's
