For the mutations and stuff, here's a summary:
Mutable genus creatures can take Biomorphs. You may select biomorphs up to the maximum number listed for each creature. The "+ x points" is the cost of the biomorph. A unique set of biomorphs on a genus is a species.
Pick bio-weapons from the list until you have reached the number the creature has, generally one per pair of arms.
3. Hive Mind Powers.
Not all creatures can have these. Simply pick the ones you want and pay the points.
Each brood may have a number of mutants equal to the number of Wounds in the brood divided by the number of species (biomorph and genus combinations) in your hive fleet. A hive fleet must have at least one species from each category, except for Fast Attack. Your army must be from the species choices in your hive fleet list.
For Warriors... it depends what you want them to do. You can give them Leaping, Rending Claws, Scything Talons, Toxin Sacs, and Extended Carapace, plus whatever Adrenal Glands would be useful for a melee-based species. Or you can give them Enhanced Senses, Extended Carapace, Scything Talons, and Deathspitter against light infantry at mid-range. Or you can give them Scything Talons, Venom Cannon, Enhanced Senses, and Winged to provide quick, mobile fire support. Tau Hammerheads? No problem. Deep Strike a couple and pump your S6-7 Venom Cannons into its rear. They can only glance, but a couple will get rid of it.
Avoid the Barbed Strangler; its Strength tends to be too low. If you take Lash Whips, only take a few, because they are no culmative. If you take a ranged weapon, try to get one with some range. Bio-plasma is fairly powerful, but quite expensive, so I don't usually take it. Flesh Hooks are self-evident, and Implant Attack is usually not too useful. All the characteristic enhancements are good when used properly; take only those pertinent to the situation.