Only package options with a matching term to the package can be set. So if you have a 3 month term package, only package options that are 3 month terms can be ordered with it. I'm not aware of ordering multiple domains for a single WP package, I think that has more to do with parking domains on a web hosting account.
The package's welcome email contains the "service" object, and the package options are available in a list of "service.options". You would have to loop over the "service.options" and then evaluate the specific option to display the option name and value (e.g. "Admin Password: abc123").
For example:
{% for option in service.options %}
{% if option.option_name == 'admin_name'}{option.option_label}: {option.value}{% endif %}
{% if option.option_name == 'admin_pass'}{option.option_label}: {option.value}{% endif %}
{% endfor %}
The above would look over all service options, and display admin name and password if those are options on the service:
Admin Name: myname
Admin Password: mypassword