About the long pinion seconds hand. I used the stock one because my 2836 set didn't have that long pinion!
Let me be specific, that is for the Jtime Alibino version for sure as it is what I have now. But I can't say for sure if it's still the case for the other models.
Again those watches are custom made and I heard they changed hands...
Anyway I did age the stock second hand as it look not good at all in stock form, but it's shape once modded is actually decent!
But I do recommend to change the hour and minute hand as those are not gen like at all.
About the GMT hand, the stock one is Okayish, maybe some new red paint and some ageing and you are good to go. The aftermarket GMT hand is crazy expensive for what it is, but if you have the funds, go for it. But in my case I used it because I already ordered it, but I would have been happy with the stock one once modded.
Sourcing the hands, I can't give any trustworthy advice as I am doing by luck. Usually I use whatever I ordered because I don't want to spoil what I bought. But I would say check with the seller to send pictures of the actual hands you will receive so you can do the usual screen checking versus gen photos!