Do I need to delete running instances, volumes, etc before I can terminate/delete a GCE account? For comparison, AWS allows an account to be terminated at any time and does the cleanup automatically.
And also, does Google offer API or command line tools to delete accounts?
If you have billing enabled, you need to contact the Billing team via this web form.
For free accounts you only need to delete your projects, these have to be emptied manually. The only option to delete projects is from the Developers Console. Here is a step-by-step procedure; please note that there is no API or command line tool for this.