This has to be one of the best treads I have read on Prune.
As a SFO working for HMG, Light Blue, I often wondered why so many Captains always carried so much fuel when all figures and experience showed we always landed fat for fuel. On my first trip in charge I added some extra fuel! Same thing happened on my first jet command flight in the real world as well!
I have always advised young crew to expect a dip in capacity and skill when moving to the left seat. The FOs need to be aware of this as well so they support new captains properly.
As a new Captain I found the hardest thing to deal with was a SFO who new best or a new FO who wanted to be given some lea way and learn from his mistakes.
Good luck and enjoy it.