I usually do a 6 gallon post boil on this to account for trub loss and the loss to the dry hop and end with about 5g into the keg. The 1oz FWH will be fine, it will be your bittering. If doing a full boil, you dont need the 60min addition (you leave the FWH in for the whole boil). 7 days is fine for dryhop. I have actually been doing 2 dryhop additions lately in IPAs, splitting them in half, then going about 3-5 days per addition.
For your boil volume, there is a settingin beersmith for boil off rate. If this is your first brew, you probably don't know it. Make sure you keep record of your pre-boil and post boil so you can add this for future reference. My boil off rate is around 1.5g/hr, so if I am shooting for 5.5g, I usually start with 7g or so. That is outdoors on a turkey fryer. If you are on the stove, it will be lower.