Welcome to Texas. You can get car tags, etc. either in McKinney or at the sub-courthouse in Plano. If I remember the order, first you have to have insurance, then you have to get your can inspected (two levels of inspection. A cheap electronic one for newer cars, and a more expensive treadmill test for older ones), and then, with insurance and inspection certificates in hand, you can then buy a tag and do the title transfer thing. I'll freepmail you some info on the homeschooling group over the weekend.
Thank you kindly. The wife is heading up to McKinney later this am to get a TX Driver's License.