Before starting a local cli-ui instance, consider following the contributing guide in order to download all required dependencies of vue-cli's packages.
Just after, you should build once then serve @vue/cli-ui-addon-webpack by running:
cd ../cli-ui-addon-webpack
yarn build # just do once
yarn serve
Then you start the ui server (based on Apollo):
cd ../cli-ui
yarn run apollo
And then in another terminal, you should serve the ui web app:
yarn run serve
For running E2E tests, you just need to run:
yarn run test:e2e
This will open a new Cypress window. You can now run all or specific integration tests.