Hi @Benny56 ,
Sitemap changes are automatically registered, but if you have made changes for SEO purposes then I would recommend submitting your sitemap to Google so that these changes are reflected in their search engine results. Doing this will ensure that your site is crawled by Google faster and that the changes you’ve made appear when your site is displayed in search results.
Redirect apps are not strictly necessary but can be useful if you’ve a significant amount of URL directs to set up. I’d suggest checking out some of the apps on offer to decide if you think this is needed.
In terms of your domain, are you removing the one you currently have or just adding a new one to replace it as your primary domain?