You can deploy the 2TB using thin and after get additional disk, convert the VDP disk to thick.
This blog post says this is a VMware recommendation, but I at moment can't found any official reference:
Because I'm deploying VDP Advanced I can have up to 8 TB of capacity; however, it is initially installed with 2 TB. You can choose to install using thin or thick provisioning. VMware recommends installing it using thin provisioning and then changing it to thick, as this will minimize your install time. Once it is installed, you can increase it to the full 8 TB.
Install and configure VMware vSphere Data Protection - TechRepublic