I like it - ending with an "a" sonority--and the letter "h" just adds that subtle, breathy continuance. I guess the "ah" ending preceded by the long "e" vowel might soften the name from the more common (perhaps previously more common) names like
John,
Mark,
William,
Paul, or
Luke. I see no reason that a boy should not be
Selah - or a girl. I would not thank that
Selah would naturally suggest need for a shorter version, as
Michael shortens to
Mike &
Suzanne,
Suzette, &
Susan shorten to
Sue.