What username/password does MAAS assign to nodes?

Question

When commissioning a new node, what username/password does MAAS assign to the node after the OS is installed?

Solution

When commissioning a new node, what username/password does MAAS assign to the node after the OS is installed?

The OS is not installed at the commissioning stage, it is only installed when the node is allocated for use. The user is ubuntu but it doesn't assign any password, instead juju will make sure that your public SSH key is installed, so when it's up and running you can do ssh ubuntu@<node>

Is it possible to specify an image or list of packages to install on a per-node basis in MAAS? Or, is this a job for juju instead?

That's a job for Juju.