1) When adding a new field to a row in a collection it would be great if it would be added to the end of the table not at the beginning. Logically, fields are added to the end or some where in between fields but usually not at the beginning. (Could also be a user preference).
2) The Add Field button should be placed in a consistent location maybe next to the + Add Row button. The way it is now it keeps scrolling to the right after each new field and eventually scrolls off the page plus it keeps making the user move the cursor to a different location.
Hope this helps.