In answer to your questions:
1. You can use the native WordPress custom menu functionality to change the menu on the top left to whatever you'd like. The menu on the top right hand side would require some modification of the default theme (although "Browse resumes" wouldn't be there if you don't enable job seeker type registration).
2. There aren't specific settings for these to be removed in the JobRoller admin dashboard, but again these could be removed through minor modification of the default theme.
3. Indeed jobs are dynamically displayed on the site as "sponsored listings", they are not saved into the JobRoller database in the same way as jobs actually posted to the site are. You can read more about the setup here.
Thanks.