I have made my own /media/sourcecoast/themes/scsocialstream/default/facebook.php ans CSS, and after upgrade, it is overwritten.
How can I solve this problem that future upgrades does not affect my custom theme?
Default view is terrible, small pictures in the middle without text, empty posts if they are picture only and so on....
Is there any documentation also which contains objects or resources from FB which could be used?
Copying the files to your templates/TEMPLATE/html/com_jfbconnect/scsocialstream/default directory should work. Once you do that, please make sure that you've cleared your Joomla cache or that you disable the cache in the JFBConnect -> Configuration area by setting the duration to 0. Otherwise, you're probably loading the cached version of the old layout.