Can't speak to the differences between Office 2016 and Office 2019. The last MS Office version I used outside an workspace setting was Office 2013.
There are a number of programs in Office365 that are not included with Office 2019 Home.
Not sure what you mean by "use primarily with USB stick". If you mean using the USB stick as opposed to OneDrive (cloud storage) and you don't need any of the other included applications, then yes. Office 2019 Home (one time purchase) is good enough (though I'd still recommend a free option like LibreOffice).