Based on decades of camping in the Yosemite backcountry, I can promise you that there is never a real problem finding an acceptable backpacking campsite. Of course, you can't be ultra-picky about what is acceptable. You may not find an absolutely flat place, but a few degrees tilt is not going to prevent you from sleeping if you are tired enough.
My advice, in unpromising territory (e.g., steep) is to start looking for an acceptable campsite about an hour, or a bit more, before dusk and either take the first OK one you find, or remember where it was, go on for another 20 minutes, and go back to it if you don't find anything better.
As @Charlie Brumbaugh said, contour maps will give you guidance, but even when the contour map says the territory is steep, you will find small flattish spaces. As for running water, to reinforce what Charlie said, the only time we have had a real problem finding running water was the summer of 2016, when the previous winter's snowpack was 5% of normal.
According to your question, you are planning to do 24 miles in 5 days -- or did I read that wrong? At that pace you will have plenty of time to explore. But I think I read that wrong.
Think of yourself as an explorer. Daniel Boone, John Muir, Lewis and Clark camped where they could. If the weather is good and the campsites small, consider not using the tent and sleep under the stars.