What are the possible options for the salesforce user type?

  Your best bet is to refer to the Salesforce api docs to know all the possible options for the salesforce user type. They do a good job of explaining the fields and their possible values. The link to the doc in question is: https://developer.salesforce.com/docs/atlas.en-us.212.0.api.meta/api/sforce_api_objects_user.htm

  I've included the snippet from the UserType field below.

Description The category of user licence. Each UserType is associated with one or more UserLicense records. Each UserLicense is associated with one or more profiles. In API version 10.0 and later, valid values include:

Standard: user licence. This user type also includes Salesforce Platform and Salesforce Platform One user licences. Label is Standard.

PowerPartner: PRM user whose access is limited because he or she is a partner and typically accesses the application through a partner portal. Label is Partner.

CSPLitePortal: user whose access is limited because he or she is an organisation's customer and accesses the application through aCustomer Portal. Label is High Volume Portal.

CustomerSuccess: user whose access is limited because he or she is an organisation's customer and accesses the application through a Customer Portal. Label is Customer Portal User.

PowerCustomerSuccess: user whose access is limited because he or she is an organisation's customer and accesses the application through a Customer Portal. Label is Customer Portal Manager. Users with this licence type can view and edit data they directly own or data owned by or shared with users below them in the Customer Portal role hierarchy.

CsnOnly: user whose access to the application is limited to Chatter. This user type includes Chatter Free and Chatter moderator users. Label is Chatter Free.