Sounds like an excellent ride, I have done it several times in February. You can expect beautiful weather. Rt 101/180 is an excellent cruise out of Matamoros. I haven't gone through Laredo, if you were planning to cross there. Matamoros customs is very professional and helpful. You will need your original title and registration, not copies, and your credit card for the temporary vehicle import sticker. When you leave the country, make sure you cancel the sticker at customs or you will have problems when you return.
On your way down, be sure to visit the Toltec/Maya ruins at Chichen Itza, Palenque, or Edzna. The societies and cities that were here in the Americas before the Europeans came were pretty unbelieveable.
When you see a barbeque (usually a cut up 55 gallon drum) by the side of the road, it's time to chow. The Mexicans definitely know how to grille a bird.
The Mexican drivers respect speed, unlike in the U.S. If you are not passing, you need to keep well to the right. If a truck driver can see over a hillcrest and it is clear for you to pass, he will put on his left turn signal to let you know. This works because once you are out of a city or town, there are virtually no intersections or driveways. Passing is aggressive but usually reasonable.
What kind of bike are you planning to ride?