That will make a good pale ale, but with only 1oz of hops it will be a little on the weak side (hop taste not ABV). I would recommend getting one more ounce of cascades, and you'll have a nice brew. In fact this is very similar to my first brew, only I used 6.5# LME, 2oz Cascades and Wyeast 1056 yeast.
If you're able to get another ounce, I'd use these intervals: .5oz for 60m, .5oz for 15m, 1oz for 5m. This will give you a nice flavorful, aromatic Pale Ale. As for the 3 gallon pot, you can just top off the fermenter to 5 gallons with pre-boiled but cool water. Your other option is to get another pot and do a split boil, but this will complicate your hop addition and double your evaporation rate.