I might disagree about the need for actnics... I bought some halides a little while back, and bought the bulbs in the 14k spectrum. I have noticed a great actinic glow along with beautiful crisp white...
I'm no expert, But I think Halides in this spectrum range give off ample of both... I love the shimmer effect that Halides have, and I love the intensity... My fish have clear shadows now!
If you take pictures in series you will see a drastic difference in the pictures from picture to picture even though they are of the same spot, and taken only milliseconds apart... You can really see the blue in one picture, and then the white in another...
The only reason I would use actics along with your halides would be to simulate dawn/dusk... personally I just use a combination of the rooms lights, then a flourescent light reflect abient light off the wall into the tank, then my halides... and then in reverse order for the night...
When It comes down to it. I think its personal preference... But I'd say, if they are already there use them...
As far as needing the chiller, I'd mount your halides and then when you have a day to check them out, turn them on and monitor them... if the temp starts to raise to high, turn them off...
Personally, I havent noticed a huge temp spike... granted Ive only got 2x 175w halides over 125g but I still need my heaters to keep my water at temp...