A very good friend and former college roommate works there. It is an great place to work so congratulations!
What advice would you give to a junior dev who is about to start his first job?
Learn about personal finance. As a datapoint I personally invest passively as in I dump savings in broad index funds (either an S&P500 or Total Market index fund) every month and completely ignore the market (check out subreddits like /r/financialindependence /r/Bogleheads etc). I prioritize in the following order: 401k employer match -> HSA -> IRA -> remaining 401k -> Mega Backdoor Roth 401k -> Brokerage account. Note that Backdoor Roth and Mega backdoor may soon no longer be available due to the tax bill. I try to limit RSUs to 15% of my portfolio and high risk assets (crypto etc) to 5% remaining is in indexes and I rebalance accordingly. Do your research and see what works for you. Live below your means and invest early.
As for the job dont worry about it and just relax for now. Make the most of college while you are still there. Take a break, travel a bit. You will learn what needs to be learnt on the job.