For gaming the 460 will be worth it, though keep in mind the MBP isn't a great machine for gaming anyway. If that's important for you to do portably, you should look at a Windows machine. There ones specifically for gaming, and you can do everything else on them too, but there are tradeoffs, including size and weight, running hotter and louder, worse battery life, and build quality for some.
I don't think the other upgrades would matter much for your use. Keep photos or whatever you aren't working on in an external drive.
You wouldn't see any difference with a 5K display unless you got up really close. That's the point of a "retina" screen--it's designed to have as much detail as your eye can resolve at a normal distance. You can drive two 5K external monitors with the MBP, though. They're bigger, so you can see the extra detail.