I think you have a good plan going if you could only get one of each. If it were my recipe I might move the Chinook to 60 min and the Cascade to 15 (but it will work fine just like you have it). The dry hops you have will definitely give it citrus but it may be a "sweet citrus." I recently made a low ABV IPA and used 1oz of Simcoe at day 8 in the primary (which I left for a week), then racked to the secondary and added 1oz of Simcoe and 1oz of Galaxy (very similar to Citra). I was hoping for intense pine & citrus, but rather I got sort of a "bowl of fruity pebbles cereal with a splash of tangerine juice mixed in" aroma (which is not a bad nose, just not really what I was aiming for). If I had my recipe to do over again I would have added some Columbus to the dry hops for a little bit of pungent complexity.
Bottom line: to answer your question, your best bet would be as a dry hop.