So here's a list of some possible sleep stops along the way. We're still discussing these, so nothing is set in stone.
1st day - Camp at Meridian State Park (78 miles)
2nd day - Stay at the Howard Johnson hotel in Copperas Cove (70 miles)
3rd day - Camp at Blanco State Park (90 miles)
4th day - End in San Antonio (51 miles)
If we do it this way, it would alternate camping with a hotel stay, and the longest days would be after sleeping in a real bed.
Also, there are some bailout options for day 3, in case we are running out of steam in the hills.
Johnson City is 14 miles north of Blanco, and could be a good bailout. It has a Best Western if needed. That would put day 3 at 76 miles and day 4 at 65 miles, but doesn't have any camp sites that I could find. That doesn't mean we couldn't stealth it somewhere, just that I couldn't find any advertised sites.
Marble Falls is another bailout if things look really bad. It's another 24 miles north of Johnson City (via our route), and has lodging. But it would put day 3 at 52 miles and day 4 at 89 miles, so I would say we probably don't want to stop here unless things are going really poorly.