Hi takenbyvultures and welcome to the forum!
The problems outlined by grafxman are very real. DSLRs
all lack video viewfinders, and most of them have poor video autofocus, awful video image stabilization and noisy internal sound.
You can certainly overcome these problems by buying a camera more suited to video - such as a
$978 GH3 mirrorless camera, a
$1298 Sony RX10 large sensor superzoom or the
$1999 XA20 that grafxman recommended - but you've already invested a lot of money in your Nikon, so it probably makes more sense to buy a few accessories than to buy a whole new camera.
Let's go through the solutions to your DSLR's challenges one by one:
Viewfinder - least expensive answer (with decent quality) is probably a
$90 Hoodman 3.2" viewfinder loupe. This will allow you to use the LCD as a viewfinder in bright lighting conditions without washing out the screen.
Stability - For what you're trying to do, I would get a shoulder rig. A tripod would give you rock solid images, but would be a challenge to move it around at a music festival. A stabilizer is probably next best, but my stabilizer spends most of its time in the closet because it's a complex piece of machinery and hard to balance and "fly". I would get a shoulder rig as the best balance between stability, mobility and ease of use. That said, I recommend the
$200 Kamerar SOCOM as the best value-for-money rig on the market today. It is a less expensive version of the excellent
Photography & Cinema PR-1.
Focus - the
$140 Kamerar FF-3 will work well with your Kamerar Socom (or any) rig. Overcoming this challenge is probably the toughest, because it requires the acquisition of a new skill, not just a piece of hardware. It's not impossible, it's just not trivial. You may want to practice before the event.
Audio - I would get a
Tascam DR-60D preamp/external recorder (on sale right now for $220), a
$27 attenuating cable to plug the recorder into the camera, and a
$330 Sennheiser pro mic with a
$70 wind muff, a
$9 XLR cable to connect the mic to the recorder and a
$15 shock mount. In a pinch, you can connect the mic directly to the camera with a
$15 Hosa MIT-156 XLR to 3.5mm transformer/adapter.
I have a
Tascam DR-40 and a pro mic and this is the approach I use. You'll get a
lot better sound than from a Rode prosumer mic, and you'll have a backup track in case something goes wrong.
Hope this is helpful and good luck with your project!
Bill