Hi Kim!
Thank you for bringing your question to the Disney Parks Moms Panel.
Disney Princess Half Marathon Weekend is the first runDisney event I ever participated in, so it will always be special to me!
Whether you choose to stop at the character is entirely up to you! Traditionally the 5K courses have had about a half-dozen character stops, but this can vary from year to year. Based on the mileage and this average, you can expect a character roughly every half mile or so. My mentality is to not stop for characters that I can meet later on in the park. The great thing about a lot of the runDisney events though is they are usually special characters that you don't get to meet often!
How long the lines are for you will really depend on where you are in the corrals. The earlier corrals will have fewer people in front of them so their lines will likely be shorter. However, the 5K is not timed and they do not enforce a per mile pace so you don't have to feel rushed and if you would like to stop for every character you certainly can. During the runDisney events, the Cast Members that are with each character also try they their best to keep moving things along because they understand that everyone is taking part in a race! As much as the Cast Members try though, the lines can still be long since there isn't as much area to stretch out the runners or characters over the 5K course in comparison to say the half marathon. I have waited for characters up to 10 minutes before, but you will wait longer than this any day in the park, so I still think it's short in comparison. Unfortunately you are not able to complete the race and then go back so if there is someone you don't want to miss I definitely recommend stopping along the way.
Please let me know if you have any other questions and I hope you have a magical race!
-Lindsey ºOº