I've lived in Coppell, currently own two rental properties in Coppell, and currently office in the Valley Ranch/Las Colinas area. The price per square foot will definitely depend on the exact area you're in, however, expect it to be over $100/sq. ft. There is no way to predict potential appreciation, however, the Coppell ISD area values have held up very well these past couple of years, some of the areas in Las Colinas, not so well.
Townhome sales have been much slower than single family detached in the areas you've mentioned. Several builders have started townhome developements (Ryland, Carmel, Avery Edwards, Positano, City Homes, etc.) and sales have been much, much slower. Depending on the exact area, but in the vast majority of cases, 3 bedrooms will have a better resale than a 2 bedroom unit.
Concerning townhome rental rates, again it will depend on the exact location within the areas you have listed. Rental rates will range from $0.80/sq. ft. to $1.10/sq. ft..
If you would like more specific information, please feel free to contact me at 972-402-4124.