I live in Houston and go to festival every year. I'd suggest allowing at least 3 days for visiting the displays and shopping. Sunday is my favorite day for both because most of the fly in people leave on Sunday and it's much less crowded.
Since you're flying in, you might want to book a hotel downtown. You won't need a rental car if you do and, believe me, if you aren't used to Houston traffic and Houston drivers you really don't want to drive here.
You'll have a great time. Houston Quilt Festival is like Disneyland for quilters
