I am considering buying todoist pro and need to know if I will be able to import my current extensive task listing?
It depends. We do have an option to export and import task lists, but they use a specially formatted TXT file meant to serve as a way to create task templates from Todoist. You could make a TXT file with a list of tasks and each line in this file would be converted to a task, but without any property.
We will consider adding importing options from known standard formats in the future.