I'm so glad to hear that Gordon would come onto your hand! I remember the days when you'd just gotten him and he was afraid to take treats from you, so you just had to leave the treat on the substrate for him. It is such an amazing moment when you get such a shy little creature to start trusting you.
A Samla sounds great, it's easily portable if you need to move him temporarily.
If there's a Chinese hamster for adoption to be found in your vicinity, he's probably as good as yours already.
I don't know if he has a medical condition, but they're quite good at hiding it, apparently. My wounded Robo has clear eyes and nose, perky ears, and was just as active as usual on her wheel, eating and drinking normally. Apart from the obvious wounds on her butt.
For Percy, I would just keep him under careful observation, maybe he needs more time to adapt to you and his new home. Maybe he had a stressful life prior to this.