Is it a mashup or a regular application?
The first sheet in your application could be this Home page.
The back to homepage button could be a KPI object. This object have a link-to-sheet properties, you can "drill-back" to the first page.
If you want to open application directly with home page, you can achieve it with copy the link of the first sheet and send to your users, I think it can't possible directly.
You will not be able to do that in out of the box Qlik Sense. If you can you will need to create a mashup.
The best you can do is have the first sheet be the home page. You could add buttons from an extension to navigate to the other sheets from here and then back to the home page from the other sheets. The only way to have the home page open is to have the user use the URL directly to it instead of going to the hub first.