Unfortunately, there is no way to create new placeholders. The footer and the header is all we have and we cannot move them closer to the top.
The upper part of you box, the top navigation and the gray bar below can not be updated with SPFx. You could possible use css to hide elements but that is not a proper solution and could break in the future. You can use CSOM/JSOM/Rest to add or remove links in the top navigation. You should use SPFX webparts to add content below the gray bar.
You can format the query string for the list that you will be redirected to, and append your own query string to it. For example, here I am using a ListViewCommandSet extension, but the idea is the same.
Once you run gulp serve, it will open the url you provided in serve.json and it will append some information to it like the following: