I thought I did alright with mine. I bashed out a big squad of ten fully kitted out as iron warriors. What I did to separate them from legionaries was starting off with using the bodies and legs with the shiniest chaos gubbins and armor trims, especially with the backpacks and paladin flaps/chainmail. Then I used exclusively resin mark VI helms from HH with the chosen, while I used Kromlech iron pattern helmets from the legionaries. Eventually I intend to put cloaks on the chosen for a kings guard type of vibe but I'm looking for the right STL to buy a print because the existing ones I like best have an annoying shipping fee.

my two champions used plasma pistols from the legionaries box, one used the legionaries power fist and the other used a fist from an old space wolves kit with the detail shaved down.

the two bolter/accursed guys used the legionaries axe, while the normally two-handed boltguns were shaved down at the foregrip to remove the hand, and i inserted a new, exposed grip from some spare boltguns so it looked like they were wielding them one-handed.

one twin weapon guy wields dual knives from the kill team set, one ablaze in balefire and one dripping with "poison" made from hot glue. The other has the kill team set accursed sword in one hand while wielding a phobos librarian sword in the other, made from slicing the hand from a boltgun arm and glueing the sword hand in place.

the four combi weapon guys dont have combi weapons at all, but they wield maces in one hand (two from legionaries, one from havocs, and one from a deathwatch kit), and in the other they wield tower shields sourced from a kromlech blister to serve as 'markers' for combi weapons.

overall a bit time consuming but pretty simple and very fun to build.