Can I add gif images for the banners and sliders? Whats the appropriate size for the same?

Yes, you can add gif images to the banners and sliders through your StoreHippo Admin Panel. The size of the gif is same as the images of banners and sliders.

For information on how to add images in banners and sliders, refer the following links:
https://help.storehippo.com/topic/slides
https://help.storehippo.com/topic/banners