Ad 1) jpg is not format for logo, it has compression. My recommendation is to use png file.
Importanat TIP! If you installed Quickstart - it has 3 different template styles. So disable/delete those which you do not use, and keep only one. Less confusion. Then you should be able to change logo in current used template style. Many users makes this same mistake, and change logo in not current template.
Please upload png logo file to /images folder first. Then just choose it.
ad 2) I guess, you have to be Joomla beginner. Becuase it's very easy to find template layout - with all module structure.
The most easy way would be to use module position named "Content Top" - where your slideshow should be published.