Everything is well marked for the first week or so of the walk and by the time that they get a bit casual about it you will have got the hang of how the Camino works and shouldn't have any problems with a bit of common sense. I did the same walk as you are planning from mid May to mid June this year. I had no map, a rudimentary guide and had no navigational problems. I heard of a German lad who set off one day, walked hard and ended up back where he started but the fact that people were talking about it suggests that it is pretty rare. Anyway, what is a day in a lifetime?
As for footwear, this year everything was dry and so shoes would be fine if they are well worn in, have tough soles and are comfortable. A heavy rain storm in the clay areas to the west of Pamplona could cause you problems but, what the hell, it's not going to wreck your pilgrimage. I wore leather boots but the weather was so hot that I boiled my feet.
Relax, take it as it comes and enjoy the camaraderie along the way.
Buen Camino
Paul