Reddit mentions of Lowepro 8 x 12 cm Case for Lens - Black

https://www.graesen.com/concerts - let me know if you have more questions. I'll address your specific questions below though.

1. Keep your bag on you or wear something with lots of big pockets. When I do concerts, I plan my gear very specifically. I might use a Sigma 17-50mm for most shots, a 8mm fisheye for effect, and something telephoto like 100mm f/2 or something. These lenses aren't usually easy to put in a pocket, but I try. When I know it's not possible, I attach a small lens bag to my belt for swapping lenses. I have something like this one (might not be the same size) - https://www.amazon.com/Lowepro-LP36978-0WW-Lens-Case-12/dp/B01C4QSBDU/ref=sr_1_5?crid=3PGZLC7ORKIHF&keywords=lowpro+lens+cases&qid=1567742748&s=gateway&sprefix=lowpro+lens%2Caps%2C156&sr=8-5 . I attach it to my belt and it has a space to store a lens and a space to temporarily hold a 2nd lens until you're ready to swap. Basically, that 2nd spot folds closed when you zip it up.
   
2. I shoot as a hobby too. I aim for next day delivery but also edited. Once 24 hours passes, the show has left people's minds and everyone has moved on. Most venues post shots later that night or the next day as a way of showing customers what fun they might have missed and to encourage them to attend in the near future. But if they share those photos too late afterwards, that excitement has died down. Chances are, someone else would have delivered photos before you as well, if you wait too long. However, since this is purely a hobby, no loss if you take your time. If you were being paid, there's more motivation to deliver asap. For me, not being paid = no pressure. I used to have that dream to shoot shows as a side job but most bands and venues already have someone for that. It doesn't mean you can't make it too, but for me, I have more important things in life to worry about. Prioritize your own life and work towards that. Faster delivery shows you're dedicated. But if you're not getting paid for it and likely won't, is it really worth it? You decide.
   
3. The band moves around, so should you. But don't make the show for the audience less fun either. If there's no barrier/pit between you and the stage, find spots that don't interfere too much with the audience. Use lenses that account for that too. Try to learn the venue and when they will or won't have a barrier or pit. Learn the bands' crowd and figure out just how crowded it might be and how crazy it'll get. Are the fans likely to mosh? Then stay to the sides and out of their way. Are you shooting ICP and they're known for spraying Fago soda everywhere? Well... at least get a rain cover lol. You get the idea. Most importantly, people will let you move ahead for a shot or 2 under the assumption you're doing a job, but if you hog their spot or stay in their way, that's just in bad taste. Get close, take the shot, then move on. Oh! and shooting crowd shots is always a plus anyway. If you can capture the band in exciting poses on stage and make it look like the venue is crowded and the fans are into it, that's gold. Stage shots without any audience shots aren't always good.
   
4. Extra advice... well, here's my technique: Shoot Shutter (Tv) priority and set shutter to about 1/160. Faster or slower depending on the light and amount of motion blur you want/like. Set ISO to auto too. Set the focus points to center only - center AF point is usually cross type which means no matter how you hold the camera, it can find focus easily. If you want a more technical explanation, use Google. Set metering to Spot metering - this will calculate exposure for the center of the shot (aperture and ISO will be automatically set). Now place the center of the shot on the artist's face or whatever your subject is. Acquire focus and hold it (back button focus is nice for this technique too). Then quickly recompose the shot to how you'd really capture it and snap the picture. This is focus and recompose. The spot metering calculates the exposure for what you're focusing on rather than the whole shot. If the stage lights dominate the shot, evaluative metering could cause your subject to be under exposed. But with spot metering, exposure will always be right for where you point the camera. Also, shoot in burst mode. If you see the band start to do something exciting, start capturing as they start and continue the burst throughout the entire motion. When editing, don't worry about the colors of stage lights. White balance for normal looking skin tones when possible. Sometimes that means the stage lights look nothing like they really looked, but it makes the band members appear more human and personal. There are times when this isn't possible or the white balance corrections just ruin the shot though, so use your judgement.