SQL Authentication can be used with AF but is not necessary. For an AF Collective, the Windows account that runs the SQL Agent on the primary SQL Server needs adequate privileges on the primary and secondary SQL Servers.
AF does not require the use of the SA account. It is not a recommended practice anyway. But this al depends on your configuration. If you installed AF making use of the SA account, then you'll need to change that.
EDIT: forgot to refresh... not the first one to answer.
There are a couple of scenarios where SysAdmin privilege is required. (1) some install scenarios require SysAdmin privilege while the install is running, (2) the users that are configuring or modifying an AF Collective need the SysAdmin privilege.
In general, I would disable SQL Authentication. However, before disabling SQL Authentication or the "sa" account, make sure that a Windows account or group has the SysAdmin privilege. (Otherwise, you will have the opportunity to practice uninstall then install of SQL Server.)
I would strongly recommend never configuring an application with SysAdmin privilege ( and never running the SQL Server service as a privileged user, such as LOCAL SYSTEM, local admin, or domain admin.)
AF SQL Dev