"I'm going to see an indie band at a very small venue and I need to be comfortable but sexy and cool. I'm a size 14, so I'm not going to be rocking a pair of skinny jeans. I'd like to wear something v-neck on top, I think. I'm absolutely clueless about what to wear."
You might want to reconsider the ban on skinny jeans; being a size 14 doesn't mean you can't wear them. Depending on your figure, skinny jeans can actually look great on plus sized women and can give us a slimmer look than flared, boot-cut do. A good compromise if you're still not comfortable in the skinnies, are straight-legged jeans. Like any other style of jeans, just make sure you get a good fit.
As for everything else? The goal is to balance looking good and being comfortable. As good as you may look in 4-inch heels, that's not exactly the best way have fun at concert, especially when there might be time spent in lines, dancing in front of the stage, or even outdoors. I recommend flats (with good support), low platforms, and for the occasions that just demand, it a low heel, will at least ensure that your tears are from the music and not the pain in your feet.