I'm with Richard Bridge on this one (got to say that, it doesn't happen all that often) Harper sounds OK, though it does offer some unkind possibilities in the nickname line. They might even have chosen it after Harper Lee, though somehow one would doubt it.

Mind you, Seven is beyond me, but when I think of some of the abominations that other "celebs" have perpetrated it seems pretty innocuous. It has no obvious drawbacks of mispronunciation or association, and should be easy enough to spell.