Is there an efficient way to export all models and their size from a workspace into a csv?
Easiest way is to use the Anaplan RESTful API's. Now with the transactional APIs you can get the model size too. Many people like to use Postman which is a free application and plenty of examples on Community to help you. Candidly, I like to use Python, also free, but it takes a while to set up your environment.