How Do I make my website faster (according to Google and Pingdom)

Hey there Gang, 

I ran my website via Pingdom Speed Checker Tools (https://tools.pingdom.com/#!/eFyjYP/flagupmail.com) and have found it difficult to fix three things slowing my site down:

I am using Tailwinds CSS, Stripe, Google Fonts, and Font Awesome. 

1. How can I combine External Javascript?
2. How to Leverage Browser Caching?
3. Serve the following static resources from a domain that doesn't set cookies?

Any experience on how to accomplish this with a rails application? 

Thank you all!

(For details view the link above, it should direct you to the specifics)