Chaos space marines will be able to kill anyone who comes close however easy to take down with long range snipers.chaos space marines are equipped with flamers: sometimes their kills will be on your name, resulting in your party losing morale.
tanks have a lot of armor and can knock down large groups of infantry.however I will add anti tank units that can take tanks down with ease.
Unlike the parabellum; anyone can and will damage tanks. You don't need anti tank infantry. Tanks also are pretty rare.
gaurdsmen aren't the best ranged units and can barely defend themselves in melee but they have pretty good ranged weapons: they will miss a lot but getting hit can be fatal.
Orks come in very big numbers but are easy to kill, but don't let them get close!
Tau however come in small numbers with very long range weapons. using speeders will be very helpfull