Some of your Questions
Designing is a very important part. The important part in which the business connects the user with it. And with the changing times, we update all our business with that and focus more on the layout and usability of it.
If you want your site to rank in Google, then you are probably already focusing on the appropriate topic, so that SEO compatibility can be taken care of. Keyword research is definitely important for getting links.
Retina design devices have more pixels per inch, so a high-resolution image design is required to fill in those extra pixels. devices all require retina-ready design.