Equalizer landing page

Hi! I would really appreciate if someone could help me with:

1. I still find hard to understand a design file. Where is the correct position for the background decoration bg-pattern-1? Do I add it to body or .container?
2. Is there an easy way to convert px to em or rem? I've just started using them.
3. How to set an image correctly, so it would be perfectly responsive))?
4. I applyed :hover on icons. How do I make the transition between colors smoother?
5. What is the best way to make a responsive website? I've got an idea what to do, but when I need to match a website to a designer view of a responsive layout, I really struggle;)

Thank you a lot in advance!