Sounds like you are going to be busy for a while. To get started, let me introduce you to several features of the Lady Bird Johnson Wildflower Center webpage. First are the two pages with our “How-to Articles”, and our “Step by step Guides”. The articles here will answer, or give you hints, for most of the questions you have asked.
The next feature is our Native Plant Database. This option allows you to search for 7,364 native plants by scientific or common name or choose a particular family of plants. Scroll down to our Recommend Species Lists and click on View Recommend Species page. Click on Central Texas on the map, and you will get a list of 156 commercially available native plant species suitable for planned landscapes in Central Texas. The Narrow Your Search box on the right side of the screen allows you to search for tress or herbs or grasses. For example, in the box, select: Texas under State, tree under Habit, and perennial under Duration. Check sun under Light requirement and dry under Soil moisture. Click on the Narrow your Search button, and you will get a list of 19 native trees for Central Texas. You can repeat this process to search for shrubs, grasses, herbs, etc. Clicking on the scientific name of each plant will bring up its NPIN page which contains a description of the plant, its growth characteristics and requirements, and in most cases images. As you check out each plant, you can note its size , moisture requirements, and benefit to wildlife. Scrolling down the NPIN page to ADDITIONAL RESOURCES and clicking on the species name next to USDA will bring up the USDA PLANTS PROFILE page for that plant. Scroll down that page to the map which shows its US distribution, and clicking on the Texas map will show you if it occurs in Erath County.
As for soil, that’s more complicated.; so much so that there are even people who are known as Soil Scientists.
I’m including three links for you to explore concerning the nature of soil.
Bachman’s Garden Care
Encyclopedia of Earth
Before you have soil brought in, I suggest that you contact the folks at the Erath County Office of Texas Agrilife Extension. They can advise you about soils and soil testing, and make recommendations about the kind of soil that would be best for the project you have in mind.