As a Developer, these are the things I look for when joining a team:
Ie. the day-to-day life is not a chaotic mixture of "do it yesterday!" ad-hoc work and massive tickets that were not in scope. Since you have already implemented Kanban, it is a good start. Optimally you will follow the format even when you are the sole developer. It will take some extra effort, but don't cut corners. Ideally adding someone else to the workflow will not affect the workflow beyond the obvious increase in tickets.
It should be possible for a new developer to jump right in by following a step-by-step (and tested!) checklist to get the basic environment up and running. Then from a stable basic env, you can continue to other repositories that are related to the work. Each repository should of course have its own readme file with instructions on setting that up, with notes if something depends on the basic setup.
Clear todo list / sprint plan
There should be a clear list where you can see the backlog, and priorities, of the tickets and expected work. It should be clear what the developer should work on next and the tickets should have good description of what is expected. A one-liner eg. "Implement product catalog." is not enough.
Good introduction / boarding
All the expected things and general guidelines should be clearly explained. Optimally they also exist in an easy-to-find document in some interal site eg. Confluence where you can always return to. This should also contain a high-level picture of the project, eg. what components there are, what kind of data goes in and out from them, what tools are used, and so on, in high level - leave the details into the repositories.
Should have clear instructions on how each component is deployed to Staging, Production, whichever. Optimally you don't need to ask someone how to deploy this to that.
Clear workflow in the versioning system
You should have defined ways how the integration goes. Ie. fork this, create a feature branch, do a PR to upstream master, get approval, merge. Deploy from Jenkins project ABC to Staging. Check that tests pass. Then Deploy to Production. Whichever style you use.