I've been here for about a month now and still feel like I'm mostly just in free falling trying to figure out 95% of what anyone talks about or how to do things. It seems like everything works fundamentally differently than it does for a smaller scale company.
Do you have any advice for short/long term success as a developer that is very new to operating in an environment at this scale?
It is fairly normal, every company has its on acronyms, processes, so I would say it is fairly normal to be overwhelmed in the beginning. There is no way you could know in advance their process.
That being said, you should have colleagues available to help you.
Take always a notebook and a pen with you. Whenever there is a word, or process, you have never heard of or are not sure what it consists of, write it down.
Now every few days schedule a meeting with a member of you team, reviews the list, and request explanation/clarification.
Take additional notes for future reference. That's it, in a few weeks you'll feel at ease with what is happening around you.
This is a gradual process, you'll keep learning in the months, years to come.
Then once you feel more at ease, you can push for initiatives, new ways to do things. A newcomer has usually always lots of fresh ideas because is not yet used to how things are done here...
Large code bases themselves don’t have to be confusing though. I worked as a contractor at Google and their system was very dev friendly with almost everything is available/viewable in a large repo with good editing and build tools.
I hope those 250 developers are split up on small teams, with small manageable projects.