Congratulations! I answered your waitlist post weeks ago. I did not admitted by Rice, either. Luckily, I have accepted the TA offer from Cornell.
I must say to you that don't worry about the tax since the annual taxable income of TA is very low. This holds true sadly in almost every country on the planet!
In addition, the stipend rates are adjusted yearly by the grad school administration to make sure you can focus on your studies.
(High enough to make a living, but low from living a luxurious life.)
The TA offer usually covers only 9 months during academic year, but you could make the rest from summer-session appointments.