I expect part of the problem with browsing the gallery is that the images never uploaded, so it is trying to reference a file that does not exist. As for the error uploading the file, make sure to have the folders have the correct permissions and the settings in the manager are set correctly. Test with small images first and work your way up. I found that on some servers the host setup may block large files no matter what you might have in the settings.
The css is a little crazy. My focus has been on the development of the functionality, not on appearance. I hope that once I work out a few more bugs and really get this running smoothly I will have time to really work on the css. If you wish to put together a nicer css package for me that is friendly with foundation, I will be happy to incorporate it with the next package release, otherwise I probably wont make any changes until I get past the beta stage.
As for favorites, it is available, but I'm still playing around with it so it may change in future versions. Currently it is a two part snippet. First you need a helper page. Create a new resource and set the template to "0" with this snippet call:
Then on the page calling the favorites you can use custom css in relation to the assets folder by:
[[!favorites.panel? &customcss=`css/favorites.css`]]
Also make sure that you assign the various pages in your settings to point to the correct helper pages. If you don't assign the various resource_id settings, sekusergalleries may not function properly.
Hope this helps.