Its a solid buy yea, thats the way I jumped aboard the ship
More or less all of the models are valid too, the Argii will become a bit outclassed when you start adding other things, but thats kind of the Light warbeast syndrome, most of them that arent straight utilitybeasts tend to get phased out once you learn that you cant have too much fury without backfires...
I STRONGLY suggest magnetizing both the Feral and the Carnivean, those 2 both makes into 2 other heavies. Buy 1-2 heavy kits and you can mix and match all you will ever need. Circle might get around on 1 extra, legion is kind a beast depending so 2 will do you good, and Scytheans/Ravagores are more worth doubling up upon then Stalker/Pureblood
There are a lot of things written about each faction on PPs own forums, and http://battlecollege.wikispaces.com/
has some useful advice and a simple way to get a gist of what a model is capable of.