Your first purchase of ANY new army, escpecially when new to the game, should be this thing :
This box (The Battle box or starter box) contains a quick rules set, and a caster and three jacks, then you play some battlebox games to learn the rules, then you buy units and solos
Of course this is just opinion, but either the Battle box or the All-in-one army box (which is pictured above, in all its glorious majesty) make good first purchases as they are great value for money and contain useful models to both learn the rules and also good models to play with when you expand
EDIT: And yes an all jack army isnt good, but thats why yiou play battle box games, where both players just use a box each, so that you learn the rules, as a completely new player the game can be daunting, trust me I know