First Big Beer

ok going to make my first big beer this weekend. going to be a left over brew for the most part.

7lb DME
.5 lb Carapils
.5 lb Crystal 20
thinking a pound of corn surgar
4 Gallon full boil batch

Hops:
1.5 oz Warrior 90min
1 oz Centennial 10 min
1 oz Cascade 10 min
.5 oz cascade 5 min
.5 oz centennial 5 min

1.5 oz Centenial Dry hop
1.5 oz Cascade Dry Hop

should be about 9.5ABV and 96 IBU

what you guys think. basically a Double IPA

It will probably work fine. The carpils and C20 both are probably more caramel than you need since your DME probably has some percentage of caramel in it, but it won't hurt. Corn sugar should help lift the gravity and dry the beer a bit.

I'd use at least a pound of corn sugar to make sure you finish low enough with all that extract. Also, since this is your first big beer I have no idea how much of this you already know but here goes:

Make sure you make a starter or at least buy enough yeast. Check the mr malty website for a reference. This is the most important thing!
Big beers get really warm so have some way of doing temp control. A swamp cooler with frozen water bottles at the very least.
For my big beers I like to try and keep the yeast in suspension by genteelly rocking the carboy back and forth without splashing much for at least a minute. I do this two or three times a day after visible signs of fermentation have stopped just to make sure the yeast don't floc out on you.
Don't dry hop right away, wait until you are about ready to bottle/keg. I mention this because I used to leave them in there for months at a time before someone told me otherwise.

the planing will be to use the slurry from a 7 gallon batch of light blonde beer I got going, so should have more than enough yeast to ferment.

Temp control really isn't a problem, basement normally is around 68 degrees.

or would you guys think this would make a more ballanced beer if diluted out to 5.5 gallons?

9.5%ABV and 95IBUs seems like a good combo to me. If anything some might argue that is a tad light on the hops for a beer that size.
Remember that even if your ambient temp is 68* the inside of the carboy can warm up probably 5* higher than that doing to the warmth generated due to fermentation. I don't know what yeast you are going to use but if I were you I would aim to try to keep it near the low sixties for the first three days or so and that would require a swamp cooler of some kind. Trust me when I say that these big beers can get away from you quickly in terms of temperature and that can lead to a whole bunch of problems, the most common of which can be fusel alcohol which can give you that alcohol burning sensation and can lead to horrible headaches the day after; neither of which you want in any beer.

Yeast ill be using is notingham