Okay for one in your paragraph you stated what your were going to do with the kroot and said two different things. So which is it. I'm not to sure about taking shadowsun, I woul noramlly take a Shas'o with a plasma rifle, missile pod, shieldgenerator, and a HW multitracker, he is cheaper and if you take stimulant injectors and he would still be cheaper. But you could optionally take both.
BSF on stealths worthless dude with an 18" range and a reroll, night fight shouldn't be a problem. for the monat I would take TW fusion blasters or a targeting array because you don't want him to miss.
I refuse to use kroot so I won't comment on them. Not to sure about the piranhas if they are going to fly along with the vcespids I would give them burstcannons over fusion blasters. If you use them with the vespids the vespids can take armoured things short of termanators but will be lacking against nids, or orks, or evern IG. basically any horde.
Seems a little thin on troops over all. I can't think of way to fix this.
The_Outcast