One of Kerrigan's abilities is to use the major attack/health values of any combat card. What about the combat card's additional benefits (i.e. Lurker's splash damage)? I assume that Kerrigan doesn't get any of these bonuses when attacking. Can anyone clarify?

I'm not familiar with too much of the expansion as yet (I own it but haven't had a chance to play with it), however, assuming the wording you use here reflects the wording on Kerrigan's card, then you are correct. Having the ability to use the major values of any card does not mean you also have the ability to use unit-specific abilities on any card. These are two different portions of the card.

Since Infested Terrans are a Sacrifice unit, they don't have a support value. Infested Kerrigan does not have the Sacrifice ability. Is it implied that she has a support value of +1? Or does Kerrigan offer no bonuses as a supporting unit (other than the Psi Storm and Cloaking card)?

okorz001 said:

No, it provides no support bonus. But thanks to Psionic Storm she doesn't really need it.

What kind of ability when Kerrigan attack? only ground attack? or both?

WYO said:

Ground only, although Psionic Storm may kill also flying units (Ground/Flying Splash Damage)

And you don't get they special skills of a unit, only its values. To say it differently: there are no minor values for Kerrigan. She always uses the major values. And there are no combat cards that match her, so the special rules never apply.