For some reason, every time I try to post an response on this thread, the wordpress site goes dead. I'll try again:
It looks like you solved your problem. You should consider adding some CSS to remove the little link images from some of your links, though, like the Exhibit images and your calendar.
If it is the case that your whole permissions problem is predicated on the bug (missing funtionality) in Exhibit that does not set permissions on created directories, then you need to look for the mkdir function in the Exhibit source and add the lines after it that set the chmod permissions. They're missing. This is fixed in 1.1.
If you don't have GD, Exhibit can't make thumbnails for you. But it you make thumbnails for your images in a subdirectory named 't' with the same names as your original images, Exhibit will recognize them and use them. So, yes, you can use this, just with a little more work - work you would do anyway if you want thumbnails on your site.
Are you using some other tool to make thumbnails? I have heard whispers of ImageMagick, but it's not as easy to implement in PHP as it seems.
Options 2 & 3 are complete in 1.1. Option 1 is in the works.
Option 4 should be easy enough to do.
Option 5 is a little more difficult, but makes sense for what you're tyring to accomplish (you don't want user uploading to the root image directory, but uploading to their assigned user directory is fine).