Grape Cabled Cardigan

This is the cardigan I am knitting for the final project of The Knitting Guild of America's course Finishing Techniques. The yarn is Louet Gems Merino Sport weight in grape, and is wonderful yarn, but very springy so that the ribs really contract. It does stretch alright but I'm wondering about blocking it. Time will tell. The pattern has the cables on the center front and just ribbing everywhere else, and is a V neck. It calls for 6 buttons but I may put in more, simply because I don't want the closing to gap. The pattern is free from Garnstudio web site:
http://www.garnstudio.com/lang/en/visoppskrift.php?d_nr=66&d_id=6&lang=us