Hi Ronald,
This blog should help to answer those questions:
What's Coming in ArcGIS Online: Introducing User Types
To answer your specific questions:
1. It is possible to change your user type to GIS Professional if you purchase a GIS Professional User Type. As they only came available as a specific User Type yesterday, I don't expect many organizations will have added them to their organization quite yet. Please note that a Creator User Type with an add-on ArcGIS Pro license will have access to the same capabilities and apps. There is no specific benefit to using Creator or GIS Professional it's more of a decision about how you want to assign licenses and capabilities to your users. As licenses can be added on to members, you can assign additional app licenses that aren't included in the initial User Type.
2. The User Type defines what capabilities you and your users could possibly have access to, but the role assigned specifies the actual privileges that are assigned to your username. Both Creator's and GIS Professionals have access to the same capabilities and can both be assigned an Administrator role. A Creator User Type has access to the same administrative capabilities as the GIS Professional.
3. A Creator is compatible with all add-on app licenses, so there are no limits to which apps can be assigned to members with this User Type.
4. When you purchase ArcGIS Desktop, you receive a Creator User Type and an Add-On Pro Licenses. User Types don't affect how ArcMap is licensed. If a Pro License was assigned to your user name yesterday, it will be assigned as an add-on license today. Nothing will change about how you use ArcGIS Pro or Desktop.
I've been mentioning GIS Professional as a single User Type when in fact there are three levels of GIS Professional, Basic, Standard and Advanced that align with the licensing levels of ArcGIS Professional. If you were interested in a GIS Professional, you would want a GIS Professional Advanced to align with your current license.
Please read through the blog and let us know if you have more questions