How easy it is really relative to your skill level ;) If you plan to purchase the theme regardless of whether or not you make the customizations, then you could of course always try for yourself and if it doesn't work you, you can seek help from a pro if you wish. AppThemes doesn't officially support customizations, however you are free to seek community based support in the forums, or as an option you can also see our
Certified Partners page if you're looking for professional help.
If your host can run WordPress, then there should be no issues with running the theme :)