Best route south???

Looked at google maps showing you to take 35 south from Des Moines. At Waco, I'd get on 77S and miss Austin and San Antonio.

I would just stay on the google route (taking I-35W thru Ft Worth) and try to avoid Ft Worth, Austin, and San Antonio during rush hours. Detouring off on smaller highways with small towns, lower speed limits, and traffic lights just to avoid a few miles of traffic will generally only add time to your travels.

I agree with taking 77 south from Waco, TX. Having been stuck in a 3 hour traffic jam in Austin, I would rather avoid the crazy drivers in the cities. Hwy. 77 south is a great drive. Most of the time, the speed limit is 70 mph. Yes, you do have to slow down for a few towns, but I still arrive home faster by taking Hwy. 77 and avoiding the congestion on I-35.

I meant to address your concern about where to stay and eat along the way. In Texas, I-35 and Hwy. 77 have many of the chain hotels and eating places all along your route.

My experience with Austin is that like most cities the traffic moves ok most of the time. But an accident or construction can really back it up. Use google maps traffic to view traffic conditions ahead of you. And TXDOT is good about using their info signs to warn about traffic issues miles in advance. If Austin appears to be a problem simply take the toll road just north of Georgetown all the way to I-10 and bypass everything including most of San Antonio.