First off... Welcome to the forum! Secondly, great advice from Kieth and Jon. These guys are good and have helped me many times along he way.
One strategy that was difficult for me to wrap my arms around early in my brewing days was the 0 minute hop addition with a hop stand. What good is adding hops when it's not boiling going to do? Well, I quickly learned that this is my favorite addition. This is your big time flavor addition. My suggestion is to take your 45 min and 30 minute additions and move them to 0 minutes. Keep that Columbus at .5 oz and bump the cents and cascades up to maybe an ounce each. And definitely go at least 4 oz for dry hop.
Another thing to consider is that Cascade doesn't bring as much to the table compared to the other C hops or most flavorful IPA hops. I'm not saying that it's bad, because I love cascade in just about any beer, but sometimes you need to bump it up in the ratio so it doesn't get lost in the flavor. Maybe a 3:2 ratiio.
After a couple of adjustment with your grains and regardless with what you do with your hops, you'll have a good beer! I love that you're into recipe design early!