Don't be surprised if he gives you a run for your money in combat. The Detachment system means that they will frequently do well on CRes, and maybe even knock a rank off from out-of-sequence shooting.
Magic, too, you may be surprised by. There are a few sneaky items in the Empire arsenal, like the Rod of Power, which allows for a great amount of flexibility. If I have too many PD, I can just switch a few. The Grey Wand is a favourite of mine for a Wizard Lord, as it enables him to get off a good amount of offensive magic. And the Lores of Metal and Fire are both nasty against WoC, as I think you'll be aware.
However, the greatest piece in the Empire army, to my mind, is the Van Horstmann's Speculum. Be VERY careful about issuing and accepting challenges, as this piece means that even a Warrior Priest can bring down a Chaos Lord and barely think twice (the WP with VHS and a GW as a favourite of mine - the bane of nasty characters everywhere).
You can expect to win combats based on kills, and the lack thereof scored by the Empire. Chaos Knights
will chop through everything, Chosen and Chaos Warriors should both do very well, and Chariots should be able to win combats on their own (D6+1 Impact Hits, plus two horse attacks, plus 2-3 crew attacks - can't remember the exact number).
Special mention goes to the Helblaster Volley Gun, which, as you will come to discover, is an extremely explosive piece. It has the potential to dish out 30 S5 hits, but will average between 10-15, and still has to roll to hit and wound. It is also very prone to Misfiring, and has a horrible Misfire chart (horrible for it, anyway). So bear in mind that the damage output of that thing is more psychological than actual damage. Whilst this isn't to say to flash your Chaos Knights in front of it, it isn't as lethal as most people think.
But as has been said, you will most likely be up against a gunline. Generally, these are the easiest types to army to beat, I find. Screen your big, nasty killers with cheap, quick units (again, as has been said), and you should have little trouble beating them in combat. Empire artillery is expensive, and can be destroyed by a reduced unit of Warhounds. If your army is fast, you'll be facing one or two rounds of shooting, which should enable you to close with his ranged units having taken little damage.
Hope this helps
.
-AFG//