HTM5 Stuttering and Preloader - can I download all at once so there isn't a lag?

So I made my first HTM5 site in Adobe Animate. 

http://operationolympia.org/Dewey.html

A couple of questions: 

1.) Can I get the animated GIF to play longer at the beginning so all the graphics download? 

2.) Is there a way to download all the graphics, so the site doesn't stutter so much?

3.) Any other suggestions for improvements? I'm new here.

Thank you.