That is a very tight budget. I'd suggest going through some second hand shops for used gear. Find a nice zoom lens so you won't need to change during the concerts, and when you have that lens you search for a DSLR body that fits the lens. Notice the need for image stabilizing and autofocus motor. Some cameras have those in body, so you don't need them built in lens, though a focus motor in camera body often makes for a bit slower focussing. Coming from the compact cameras makes any kind of DSLR autofocus seem lightning fast to you, so not a big worry at this point.
Most of the time you won't be needing a flash, but that depends of course on the the type of music festivals you'll be covering and what else you'll be photographying. The stage and bands are usually lit well enough. But of course you already know this all.
You said you don't have a problem of long distance to the bands, so I guess even a 100 millimeter lens might be long enough in your case. No harm done if you find a longer than that. And for wide angle you would perhaps like something near 20 millimeters. Note: talking about cameras with APS-C size sensor here. Just for an example: a new Sigma 18-200 mm zoom is currently $350 in B&H so a used one (if you can find one) would not cost you too much. And then you'd have some money left to buy a used body (for this particular lens it is a Canon of APS-C size) and maybe a small bag to carry it.
As long as you only aim at getting imagery for your blog, the camera body is not of extreme importance. But better cameras make less noise (visual image noise, not talking about sound) and you will want that when you get more money. For your gig that's in three weeks, I say your best option within budget is to go roam thru the used gear shops.
And to answer your question: No, a Nex 5 is not a camera for your needs. You will want to have the added stability of having the camera up pressed against your eyesocket. Lens for these cameras weight often the same if not even more than the camera body, so you will not be holding it the same way as you keep a compact camera. Viewfinder is good for framing too, much better than a rear lcd-display at arms lenght. And an entry level DSLR camera is not too heavy either. And finally, carrying a DSLR on you the other photographers won't be looking at you like you were an alien or a simple tourist.
A sample photo taken with a zoom lens at 70 mm and cropped a bit to show approximate 100 mm view (which is about 150 mm in 35mm equivalent). I was standing in the crowd near the mixing table. The band is "Him". My camera plus two lenses total cost 10 weeks ago was about $650 if using direct currency converter (it was €500 in my country) so I'm right there with you, only I don't aim at more quality than just what pleases myself...
Sony A37 + Sigma 70-300, 1/200 sec, f/5.0, ISO 800, Click here for larger image