GitLab is so overloaded right now that the ngnix server is returning 503 Bad Gateway. Do they have the capacity to handle all the projects being moved over from Github?

We've had to do this before. Remember when Sourceforge tried putting adware into open source downloads? Many projects left Sourceforge then. That was tougher. Github to Gitlab is easy.

Microsoft has put adware and spyware in their operating system. We have to expect that they may try something like that with Github. They may say they won't, but that's non-binding and meaningless.