I think you've reversed the N/S hands in the display auction. I blame the 1=1=4=7 hand for bidding only 5♣ over 4♠X. I'd rather shoot 6 than bid 5, but pass or 4nt or 5♦ has some appeal. For that matter, 4♦ fit jump over 2♠ might have been the winning action.
But yeah, the slam is only around 50%, so this isn't really a blame game.
Agree - this is a very thin slam and it's not like you can even get a friendly lead. Don't worry about it
The given auction is reasonable as well, though I might try 5C instead of 3C to show the huge distribution (plus put pressure on the opps in case they have the HCPs). Not sure whether South then bids 6 on the actual hand (IMO he shouldn't).