Organisations can have an unlimited number of Welcome Kit accounts/licenses.
A few details:
1/ When you create a new member, they receive the following email inviting them to create their account and set a password.
2/ By default, we try to retrieve an avatar from Gravatar.
If no avatar can be retrieved, a default avatar will be displayed (and we suggest you upload an image to improve your user experience!).
3/ By default, the alias generated will be firstnameSurname (e.g. "johnSmith") - you can of course change it!
If you have Admin status, you can easily invite new members to your team via Settings > Members (by clicking your company logo at the top left):