It will turn out just fine.
As far as the cascade addition goes. You could do just the ½oz. It sounds like you'll be planning on brewing it again in the future. If it isn't enough then try using more hops for that addition the second time around.
Make sure that the AA% that Beersmith is using matches that of the hops that you have. Not a huge deal, but you'll be surprised how it can change your numbers.
Some history on that recipe. Blame the IPA I'm drinking if I start to ramble.
Back three years ago when I was a noob, I swore that I would never buy a pre-made kit to brew. This was after the 2 Mr. Beer brews I made that got me started. I was brewing a 5 gallon batch every weekend from either recipes that I found in books, magazines, or on the internet. It got me thinking, "Hell, I could start making my own recipes." So I started coming up with stuff. I made some pretty bad sh*t. Read, a single hop (fuggle) IPA that had so much alpha acid content that I could feel my teeth getting smaller with every drink. I always let my roommates try each batch, they always had mixed (poor) reviews of my hand crafted noob-recipes.
Finally comes the above recipe. I decided to KISS on this one. Like all my beers at the time, I had this one on tap when my roommate's buddy stopped by for a visit from out of town. He asked me what I was drinking so I told him it was some homebrew and offered him a pint. He accepted and I pulled one for him. Few minutes later he says, "Man, I was just trying to be nice when I told you I would try your homebrew. But, this is f*ckin' good, can I get another one of these?" Right then and there I knew I finally came up with a winner. It's been popular with everyone that I've given it to so far. Even my dad, a Corona is the only beer out there drinker, keeps asking me if I have any of it to give him. One time I added some blueberry extract at kegging time, and it really took off. So, I've been adding it ever since. I've been growing some yeast out of a bottle of Sierra Nevada's hefeweizen and I think I'll try using that next time though. [/drunckin' rant]