Some sub priorities
- add as much automated testing and pre-running as possible. Use a tool like GhostInspector to add E2E tests quickly
- definitely upgrade in steps, 14 to 16. Try updating to 14 now and see what breaks. Then make a list of libraries or modules to refactor. Dont worry about 18 yet.
- In my organization node-sass has been a blocker for upgrades, along with fsevents. Try to rip those out completely if you can
- If there's any small parts of the app that can be broken out into its own service, now's a good time to try that. Often those smaller parts can run on Node 16 easily
- Good time to implement Prettier and Eslint.
Big thing is you're introducing a "platform" initiative into the organization, get everybody in the mindset of small improvements and upgrades done often. Maintenance should be everybody's job