Taking all of the Axis units from the Core set plus the original walker plus the Zombies is a good idea. With just 2 new purchases you'll be close to a 200 point army, for example: Core set units (127 points) + Ludwig (40 points) + Zombies (31 points) = 198 points. If you are willing to invest in another unit, you could also use Core set (127) + Lothar (Artillery walker, 36) + Zombies (31) + Beobachter (from the Sniper and Beobachter set, 5) = 199.
As an alternative, you could get the Axis Hero pack and the Zombies to get the following army: Core set (127) + Stefan (Hero fom the Hero pack to join the Sturmpioniere, 18) + Zombies (31) + One of the Zombie heroes from the Hero pack (24) = 200. A nice army, although some will dislike it because it lacks another walker.
Perfect! i'll order an axis hero pack!
Thank you very much for answering and helping in my purchases!
Thanks to Cloner 4000 too!!
p.s.: another question… which is the best shop in the web for premium minis? (i know dust-models of course!)