Image Setting Defaults and Privacy Plugin/Hack?

I’m pretty sure this should be an easy fix, but not sure what files to check first. With the default install, when you upload an image, the image settings default to a thumbnail size of about 128x85px (depends on original image dimensions of course) and sets to “Use thumbnail” “Not Linked” etc. I’d like to modify the thumbnail size and change the settings to “Linked” to make things easier for my non-pc savvy family. And just quicker for my own personal stuff.

Also, is there a hack or plug-in available to make all posts and info except a “Greeting/Log-in” page unaccessible unless logged in? I set-up a second blog as a Family Bulletin site and it’d be nice to be able to more tightly control access to the info.

Thanks,

Diana