Your grain bill looks good to go for an IPA, but I'm not so sure you'll hit that 1.091 from the grains alone. In order to hit that gravity, you'll need a 92% efficiency from your runoff. Since this is your first AG batch, that would be extremely difficult to hit. Heck, I actually don't know if I've ever met a homebrewer getting 92% efficiency from their system. I would calculate your recipe based on a 70% estimate then after you take your OG, benchmark off of that for your system. It will probably improve a bit as you get into the swing of things. If you still want this to be an imperial style, then I would recommend adding another 2 1/2 pound of 2-row and leave the other grains as they are. This should yield around a 1.080 OG, which puts you well into imperial territory.
On the hops question, anything you add prior to the last 30 minutes of the boil is not going to yield a lot of those flavors like orange and tangerine notes. Most, if not all of those hop flavors and aromas will be driven off in the boil. What really matters on the side of flavor and aroma are those later additions...especially the final 15 minutes or so. The Amarillo and Cascades also impart citrus note, which play really well in IPA and IIPAs.
Don't be shy on those dry hops either
Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in beer.