Yes, starting from the extension-cookiecutter-ts is a pretty good plan. It will start with a serverextension, if requested, whereas a mimerenderer usually will not have a server component. It should also theoretically just require a python -m pip install -e ., which would handle the initial nodejs tasks, but indeed, for contributing to the collaborative hallucination that is a modular client/server application, there is a bit of boilerplate, as the goal is for end users to have a working system from PyPI-published packages.
But otherwise: no, unlike toolbars and menus, the launcher has not yet received a “configure-by-JSON-schema” treatment. There are a few other tools, such as jupyter-app-launcher, but if you are going to be doing anything else custom, the overhead your seeing might be worth it vs an added depdendency.