Things to make sure you do if no travel company is to get trip insurance figured in the price. One thing that we do as well is get a security guard for each night. Most of these things can be done directly through Disney. Gail is the person you will talk with once you start the process. She is from Texas and was once a choir director in Texas. She has been there a long time and knows how to handle a trip from a Texas band directors point of view. She's great.
Also, as far as marching in the parade, the earlier you submit the request with all the required documents and pictures and video, the better chance of being selected for the date you want to march.