You have to add the Administrator user role in the security of Expenses module. Then under project security you can find the Administrator user role for Expenses module.
For second point, Just right click on the page where you will get the screen as below
There select building block and search for Pageheader Default. Select Pageheader Default , you will get the screen as below. There you can change the tilte and delete subtitle
For the Note, you dont need to create domain model. It is the entity already existing in Administration Module.
In Simple, In Modeler, Use shortcut key Ctrl+G to open search lookup where you type AccountPasswordData. Then click the entity, you will be able to see the domainmodel.
As Srilatha suggested,you need to create a Module role in Expenses Module.
For better understanding , just sharing the below documentaton about Module role and User role
Sorry for the late reply.
For third point,
Add reference selector by right click on the page and select widget which use the existing UserRole_Select page from the Administration module.
Add two Switch widgets and mark the Blocked and Active attributes of the User entity.
The Save button triggers the existing SaveNewAccount microflow, from the Administration module.