Some basic information that might answer your questions:

MINI PROFILE - You can change your mini-profile overlay image by clicking "edit profile" and navigating to the "personal" tab. Towards the bottom is a box labeled "mini profile background." You can paste a link to an image that's 250px x 250px in size. Imgur is a great site for resizing and hosting images.

This is also where you can insert links to your character's application and tracker. Just insert the plain link—no code needed.