Go to the topline menu Project/Project Settings/General and tick the option to 'scale clips to project dimensions when adding to sequence'. You can always use Motion on individual clips if you want to adjust zoom/position after the automatic result.
You might also want to investigate 'automate to timeline' options from the project window (click the second icon along from the bottom left of the project window to get into Icon View, drag the pictures around into the order you want, then click on the tiny black triangle at the top right of the project window and select 'automate to timeline'. Great way to get loads of stills onto the timeline without too much work.
