Here is the website homepage for IATSE, the national union for stagehands and movie crews. http://iatse.net
You can find most of what you need to know about "the bidness" side here. Search through it.
If you see at the top of the site, you will see “Local Unions.” Find the one in your area and give them a call or send an e-mail. Tell them you are doing a research project for your class and could you talk to someone if they have the time. They might have a packet they can send you.
Search through the website. It has pay levels, etc. There are many many aspects to stagecraft jobs and scenic/lighting/costume design and Various stage-crew positions.
Two of my lifelong friends are professional Scenic Designers. Both are successful and near the top of their fields. We started out together in a small Community Theatre. They worked their way up from the very bottom.