I've been in a position similarly unenviable to yours. It's exciting but stressful. Even if it all feels incredibly high-priority, don't burn out; it's a marathon not a sprint!
I've been picking through issues and working on fixes locally to try and get you bundled-up PRs that use the systems and conventions you've already established, instead of just taping discontinuous new on top of everything. However, despite being a grumpy old PHP and JS veteran, I'm somehow a relative newbie to Symfony and Stimulus, so I hope I'm not doing more harm than good lol.