Tbd:
It's a one-off payment, yes.
It is worth having more than one person with Thievery and Medicine (and other things) IME.
In the APs, it seems to be fairly standard to have traps all over (so if someone fails to disarm one, you need someone else to try or you get a spike through your foot)(yawn, no idea why they put traps in RPGs).
Similar for medicine, you want to heal people between fights and that's 10 or 20 minutes per person. If one person is doing that, it's an hour or two. And at low levels you may fail, later on you get Assurance (Medicine).
Touching on Traps (and definitely just my opinion here, not meaning to cause friction), I think where this goes wrong is when it comes down to a single person making a d20 roll to disarm it. That's not dynamic, and there's no tension in it. However, my limited experience with the Hazards component of PF2E makes them seem pretty dynamic with lots of different skills that can be used to overcome them.
That being said, I couldn't agree more about Medicine, unless we have a Champion or another class with focus based healing (I can't remember any others ha!)