I wouldn't worry about the GSP. It hasn't gone the way of the Irish setter just yet
. At four months, there are alot of stuff you can teach it. Too much stuff to type. There should be stickies for this kind of stuff that repeated over and over. But a few pointers:
Get a good book. I recommend Delmar Smith. Read it cover to cover. This will give you an understanding or basis of bird dog training.
I can already assume that the dog is well socialize since you live in the city. But you have to exercise the dog everyday. You'll want to steady the dog on point till the bird flushes (steady to wing) or when the gun goes off (steady to shot). Steadyto shot is actually safer but alittle more work.
Next will be introducton to the gun. Alot of different ways to do this but if its never been around gunfire, do not take him to a firing range unless you really know what you're doing. Best to avoid it all together. Avoid firecrackers.
You will also want the dog to quarter (crisscross the field). Then back or honor (if the dog see's another dog on point, it stays back and not jump in and point the bird for itself. Bad things happen. Other dog decides to compete then runs infront or flushes the bird. Owner gets mad at you and your dog. Not good when everyone is carrying firearms.)
You already got the retrieve down which is one of the biggest headaches most dog owners go thru. It's not really that hard but takes some time. Take the first few months very easy. You can train perhaps 5 - 10 mins daily then layoff for a couple of days. As it get older just reinforce what it knows. I like to do that twice during training. If my dog knows it, then I make sure she does it - I never give up or give in until I'm satisfied or the dog thinks it can get away with stuff. Everyone talks about Patience in bird dog training.
Goodluck. The only hard part is introducing the gun and that's relatively simple if you do it correctly.