How to extend the number of line items allowed in an existing template (100 is the cap right now) or if I must create a new template to achieve this how would I go about?

Hi - if you click All, it should show you all tasks. There is a limit of 2,000 though and that you cannot surpass. Are you not seeing an option for All when you click the drop down by "showing"? If not, I'd contact support.