Impact of neighbor sites on SEO and a new design

Hello friends, I am a business owner in the haunted house and escape room games sector, and I am also an interface designer. I handle the HTML, CSS, and design of my website myself.

1. Question: I have a website called reaxiyon.com and I use a hosting package from the company Isimtescil. I checked the other sites on the server I am hosted on and thought they might be problematic, but I don’t have much knowledge about these topics. Do you think I should change the hosting package I am using?

2. Question: I want to completely overhaul my site’s design, files, and link structure. When I upload the new site to the FTP, what should I pay attention to regarding redirects etc., and will such a change affect my search rankings?

3. Question: I have a great domain consisting of keywords that I can use in the haunted house sector. My main domain will remain as xxx.xxx, but how can I utilize my other keyword-based domain for SEO?

4. Question: What kind of path should I chart regarding my website and SEO? I am starting from scratch and need your suggestions and recommendations.

Thank you.