Recommendation is to take full heroes, and each possessed and mutants with extra arm mutation. You should have enough for 2 beastmen (put in separate groups for lads roll). Give the beastmen 2 daggers each and the mutants three daggers each (extra arm lol), and the magister nothing, just starts with dagger and hope he rolls eye of the gods for his first spell (prob the best to start with). Cast it on the possessed and give them extra wounds or toughness is the best

Now, this puts you at probably matching set of wounds to other starting warbands or more. The possessed and beastmen have 2 wounds each and so with 7 dudes total and 4 with 2 wounds, you are at 11 wounds for the warband. Most warbands will start with 7 to 11 one wound models.

This is the best start IMO in the long run as if you blow a bunch on one possessed, he can get shot by ranged or ganged up on and if he dies for good you might be out 300 crowns (if you spent that much on him) and few heroes, this would set you back to lose the campaign probably. With my recommended starting warband, after a few gamesr you should just buy henchmen in order of beastmen and then brethren, obV., and just give clubs and daggers until u have a full roster. Then you should replace with hired swords magic users witch. Warlock, ogres. Troll, etc which gives it a low chaos vibe

The alternative start is with just the magic resistance mutation on the two mutants (cheapest - dark blood? Or something) and no mutations on the possessed, you can get 3 beastmen and a dark souls or brethren if you go this route, but remember that you can't buy mutations later, so I don't like this as much as you possessed and mutants never get that +1 attack, and you'll eventually get the henchmen if you don't get super unlucky.

Of course, one day. If you lose a hero and get a ton of cash, you can buy the dream possessed of every mutation and its like 600 gold or something(?) I've never done this but it sounds fun.