1. How do I prevent logos to be oversized? Is there a way to make sizes convert automatically into any standard? I am not a designer, I just grab an image from the internet to my convenience.
Use your graphic editor program to re-size any image to the correct size - - such as photoshop or any other

2. I tried installing Spanish pack, I have uploaded all files yet I do not see where to choose the language.. I havent found any documentation that helps me do correctly the installation.
admin > Localization > languages > set as default


3. Where do I change the Sales message and all other default information?
Sales message -
https://www.zen-cart.com/tutorials/i...hp?article=127

Use tutorial/FAQ's link top right and search for others
Can also use dev tool kit
https://www.zen-cart.com/tutorials/index.php?article=39