How do I protect my Git codebase from build breaks?
If your code is in a Git repo on Visual Studio Team Services or Team Foundation Server, you can create a branch policy that runs your build. See Improve code quality with branch policies. This option is not available for GitHub repos.
Can I use the CI trigger with an External Git repo?
No
Can I chain builds so that one build triggers another?
Not yet.
Do I need a build agent?
You need at least one agent to run your build. Get an agent.
I can't select a default agent queue and I can't queue my build. How do I fix this?
See Scale out and administer your build system: Manage your queues