For self-hosted GitLab instances run on a smaller scale, there should not even be a chance of performance hits :).
Just to give a good overview of what GitLab is offering for both self-hosted as well as our hosted solution of GitLab.com please look at https://about.gitlab.com/features/
I am happy to hear that the CI/CD integration, which is our native solution for CI/CD and beyond is being well received! We want to persuade not force users to use our native solutions.