http://codex.wordpress.org/Moving_WordPress to move the site
http://pixelentity.com/wordpress-search-replace-domain/ has worked like a charm
you could put his new wordpress site on his domain in a folder i.e wp once the transfer is done tested and working enable it from main index
inbound links if different will be 404 errors
you could try this
https://wordpress.org/plugins/simple-301-redirects/ i haven't tried this plugin though