Before responding to these question, let me note that I did Rabacal to Coimbra over two days. The distances estimates I used would have made doing it in one leg just under 30 km, which was well over my personal target. My notes indicate that I actually walked over 32 km, but that included exploring the Roman ruins at Conymbriga. Your estimate of the distance seems a little short to me. I haven't bothered checking the rest of the distances, but even expressed in miles, that particular one looked a little shorter than what I had done, so I did the conversion for it. You might want to check the others.
Yes, villages have fonts. It seemed to me most were marked to indicate they are either untreated or untested. I don't recall any being marked non-potable.
I found booking a day ahead worked, but I cannot tell if that will work for you. Try it, and if you need to, adjust your pattern.
I don't recall there being any particular difficulty getting out of Tomar. There are a couple of different options on leaving, and I chose the route closest to the river. I don't know how well the other options are marked. Generally, the marking was generally good all along the CP, so I expect that you would have no difficulty on any of the options leaving Tomar.