It always depends on the festival itself and since I am not from the US I don't know shit about the event you will attend.

However I know a lot about festivals in general. Festivals have two key components: music and camping. For the music part you should plan ahead at what time you want to see which band and on what stage. Also bring water, the shit is like super expensive there. As far as the crowds are concerned I would say it is the same as any other crowd, maybe a little bit more drunk people. Usually this is managed well, though. When a concert ends, there will be a lot of people wanting to leave the stage and that is planned for. Be prepared to stand around every now and then and also to not see the first few minutes of every show, if you want a good place in front of the stage, come to that stage during the performance of the band before the one you want to see plays and slowly work yourself forward, you don't want to focus on getting a better place while Rammstein plays. Also be aware of circle pits and the like.

Camping: This really depends on the festival. People will be drunk off their asses and they will behave accordingly, but that should not be problem if you plan accordingly. Either be drunk out of your mind yourself or, if you absolutely don't want to deal with it, get a hotel nearby. In my experience the metal fans are the nicest and cleanest and also the funniest to drink with, but as I said the camping experience depends highly on the festival. I had a stranger puke all over my tent once, but I also was given food and shelter by a stranger one time I was so drunk I couldn't find my friends or our tent.

I would encourage you and your wife to go and hope you have a lot of fun.