use elevation to your advantage. Having less enemy air units around means your tanks will have fire initiative on the zerg.
Firing from 2 levels higher = they will never see you fire.

As for kerrigan, focusing fire on her would be the best option. Banshees + BC combo with a science vessel escort for repairs. SCV's would help too.

Depending on which protoss upgrade, (armor or weapons) upgrade those first.

I took weapons upgrade, which upgrades all attack speeds. The only way to beat Hard/Brutal easier is to capitalize on your upgrade you've made so far.

I did this mission with fully upgraded vikings, which took out air units so much easier with Science Vessel support for repairs.

I also researched the mind control beacon to MC zerg units when its capable. Awesome stuff that tower.

Don't know which you took, perhaps if you list it down i can recommend which path to take