Is the Stormclaw box a good place to start collecting Orks?
It's a good start but, to be honest, is not very good in the long run.
It's good in that it gives you a great introduction to the game of 40k via the campaign scenarios being nice and small. It also provides you a taste of a few different units that each play differently so you get a feel for a couple playstyles of orks. Long term though, you may find yourself not using Kans and I rarely see units of normal Nobz on the table since there's better options.
Finding an old Battleforce or the limited Ork MekMob box (http://i.ebayimg.com/00/s/MTA5MFgxNTM4/z/KYQAAOSwirZTxdJb/
$_35.JPG) would provide you with better long-term units than those found in the Stormclaw box.