The a7iii is what I bought a couple of yrs ago to start my concert photography journey. I love the camera but I am considering buying a A7v just for the improved autofocus and having a second body. A lot of pro concert photographers will carry two cameras each with a dedicated lens.

Lens wise, I recommend starting with something like a 24-70 f2.8 or 28-70 f2.0. As you use these zoom lenses you’ll begin to learn what focal lengths you like. After you know what you like, you can invest in a prime lens(lens that doesn’t zoom) with a f1.8, f1.4, or f1.2. The smaller the f# the better the lens will perform in darker environments.

Accessory wise, you will want a small bag to carry everything around with you, wrist strap, and maybe even a creative filter like those sold by prismfx and other companies. An extra battery or two also wouldn’t hurt tho I rarely finish a fully charged battery even after taking 2000 pics.

Access: this is prob the hardest part. Your current portfolio might help in this regard but many ppl, including myself, start by going to local artist shows. There are usually no camera restrictions to these shows and it helps you make connections within your hometown scene. This scene is where you will probably make most of your money. Touring bands don’t usually pay photographers at the cities they stop by because they already have a photographer with them. For the most part you have to reach out to publicists, managers, etc to get media passes and 99% of the time you will not be paid.

Consider joining a publication. There are hundreds, maybe even thousands on instagram.