[rintinglen]

You seem to be going with a loyalist version of the Alpha Legion. Having fought the Alpha Legion a couple of times, I think you will find that your army list doesn't do what you want it to.
Once I knew that all his units would be infiltrating, I turtled up in the middle with my Heavy support at the rear and my own assault troops ready to counter-charge. His lack of heavy weaponry in the first game made my termies murderous--they killed something like 18 CSM and two aspiring champions, between them and my Chaplain-led Assault Marines, over half his army was dead by the end of turn three.
Those persons telling you to reduce your squad sizes are misguided. Infiltrate or no, your troops will definitely face the prospect of at least one turn of rapid fire. Even an IG squad can generate a bunch of shots. Just a couple of '1's or '2's and your capacity to inflict damage is greatly reduced. Especially if you have the misfortune to break and fall back (yeah I know, "And they Shall Know no fear" but you still have moved back 7 inches which probably prevents you from rapid firing back at your persecutors.)