Congratulations on embedding Tableau dashboard in your html file.
The good news is it sounds like you're able to do a successful embed under your own login.
That's a good first step starting point.
Infinite loading screen question:
Did you make sure people who have been granted view access can properly see the dashboard?
Make sure people who are supposed to see the dashboard have been granted the appropriate access?
I haven't personally done it before. For research purposes, you may want to try explore this.
You may want to work with your network administrator and tableau server administrator to pull this off.
Share with us how it goes?
This one may be more easily resolved.
I took the following udemy course.
Check out the udemy courses, and discounts.