If you just want melee fighters, I'd go with armored (like armadillos) 8-legged spider-like creatures. Not necessarily insects; but similar looking.
The legs end in a hard hoof, but that is like the heel of a hand; they have retractable opposing grasping digits there (like a cat's claws are retractable) that let them wield weaponry, climb, etc. These can be tipped with claws that can be used for fighting directly.
Like spiders, they can disconnect damaged legs and regrow new ones. The body part can carry weaponry. The eyes are arranged for 360 degree vision in the horizontal plane, and nearly that in the vertical plane. They have infrared and ultraviolet vision. You can't sneak up on them.
Hearing like a bat, with echo-location -- Echo location in a bat is so much like vision they can fly through a pitch-dark room with lengths of string hanging from the ceiling, and not touch any of them.
Pinpoint throwing accuracy of knives, rocks, grenades or anything else over a 100 yards are so. If a quarterback can do it, they can do it better.
They can stand and fight on any three legs, two in a pinch.
The can spew poison or disabling liquids, like skunks and bombardier beetles, perhaps lethal poison like snakes, many insects, and even plants.
They have reflexes as fast as the fastest animal on Earth, whatever that is. That lets them wield a shield or buckler (small shield) with extreme accuracy against arrows, spears, knives, or thrown rocks.
They are smart enough to don steel armor if needed.
Needless to say, extremely strong for their weight; I'm not sure which mammal holds the record, but like that.
Perhaps they have tough thick hair all over their bone armor like a lion's mane; the volume of it protects the lion's neck from bites. On this animal, it can cushion the blow of projectiles and such.
I would ground your genetic engineering in Earth reality and genetically proven evolved battle adaptations, for both offense (like predators) and defense (like prey).