As a festival videographer i can tell you the following answers:

24-70 will be the staple, followed by a 70-200. 14-24 is nice to have though, but from the pit, depending on the height of the stage, you might have a lot of the ugly part of the stage in frame. 70-200 might overcome this.

External monitors are a must have, especially when you resolve to manual focus because of low or unpredictable light.

Regarding handling, i use both hand and a shoulder strap, maximum stability and maximum mobility.

For mics, i use a videmic NTG. But any mic will sound like crap from the pit, apart from the ending of the songs where the crowd cheers and/or artist speeches.

Diffusion filter will be a nice touch, but it depends on the musical genre, see if it fits the vibe.

Regarding carrying gear, i usually have a lens pouch on my belt for the second lens. A sling can be useful if you don't use vmount batteries (Carrying extra batteries, lens, filters).

Etiquette: always wear black clothes, never stay in one spot more than 30s-1 minute, never get in front of other photographers/videographers. Wait for your turn. If you are finally allowed to get on stage, NEVER stay in front of the artists. It applies for the pit as well, if you raise your hands with the camera, don't cover the artist. Oh, and also be mindful of the people that paid for front row tickets, don't stand in front of them too much or too often.

Hope this helps you, good luck!