when you create a project via command line do you need to specify a billing account. gcloud projects create.
To change the billing account do you need to user UI.
Yes you need. After you create a new project with
gcloud projects, you need to link it to your Billing Account using this command:
gcloud beta billing projects link PROJECT_ID --billing-account=ACCOUNT_ID
The same command as above can also be used to change Billing Account for a particular project.
To get the ID of your Billing Account, you can use
gcloud beta billing accounts list.
Note: the appearance of
beta here is because the whole set of commands for billing is still not marked as "GA" in the SDK yet.