CB Connect provides fields that can link to some of the social media sites if they've linked their social media account to CB. Beyond that just use a text field for them to supply their social media username then format it using the layout parameters as needed. Example as follows using layout.
Text Field: cb_facebook
Parameters > Profile Value Layout:
Code:
[cb:if cb_facebook!=""]<a href="https://www.facebook.com/[value]">[value]</a>[/cb:if]
They'd provide whatever their Facebook nickname is to cb_facebook and it'd format it into a link. You can use whatever HTML you want so if you want it to be a Facebook button or something you can do that.
As for putting it above the gallery like that there is no option for that as there is no tab position there and the gallery tab can not have fields added to it. So you'll need to find a more appropriate space. My recommendation is inside the canvas header, which will display to the right of the avatar.