I start my first "real" job on Monday. I will be one of roughly three new junior full stack developers on a team of 15 senior devs. The company has a casual dress code and they allow headphones. What should I expect? I want to grow and I don't want to be a nuisance, I also want to earn a reputation and become respected when I do have something to say.

Be yourself, dont feel attacked when somebody makes comments about your code and dont put on headphones completely, I usually wear them either half or completely with a low volume so people can still reach me.
I recommend avoid using them for sure in the first two weeks, you dont want to close yourself of from your new colleagues.

Don't test in production, don't drop databases, use git versioning (but don't commit passwords and such),.. And you'll be fine. 😁

Don't try to impress or anything, just do your job, maybe do some 'overtime' or work on projects you are into after hours etc. Suggest improvements (if it's really an improvement amd not just a change, they'll respect that)

Get to know them, but during breaks, not during dev-time, be genuine and deliver. Ask if you're not sure about something. Let them know you're interesed and such. Focus while working, put on headphones but not all the time (so you don't give the impression that you're closed off). Dress casual, after a year or so you can start to wear sandals or shorts (who knows)

Hard to say really, just be yourself. Developers are a-like, you'll probably feel at home after a week.

First, congrats! You're there because you deserve to be, so dispel any sense of imposter syndrome, because it will only hold you back.

Secondly, don't be afraid of a challenge that seems like it should have been given to a senior dev. Research every little thing you don't know and become a highly localised "expert" on everything that your individual tasks/tickets involve.

Don't be afraid to ask questions, but ALWAYS do your own research first, then ask your question, showing what you know about the problem already.

Lastly, read your error messages. Actually read them, then google then if you still don't understand. Figure out exactly what the error is communicating. It's embarrassing when you ask for help, only to have it pointed out that "file not found" probably means the file you're expecting isn't where you're looking for it. :p

Oh yeah, and have fun. It's sounds like a great spot, especially for your first real gig!

Thanks everyone!

Awesome comments here!

I wish you a lot of fun and a good start!

Thanks @maysi :)