Hello Roi,
For your First question, Please read the documentation to how to use slider and images. Next, yes, the default option is “Select a category”.
For your Third question, the changes you have made will not affect latest posts and anything in the Theme except Typography. And If you Click the Reset options button, the theme settings will revert to default. So if you don’t click the reset button, theme options panel won’t change the logo if you have uploaded any logo image.
Could you please give us your blog details URL and temporary login credentials(username &password)? Our team will check your site to resolve any problems.
Note: When you send your login details use the “Set as Private reply” check box before submitting your details.
Thanks.