(...)
1) If at least one player goes all-in and there will be no more betting action (e.g. 3 players in the hand and 2 are all-in) do the players HAVE to flip both cards face-up whilst the rest of the street is dealt or is it a choice thing?
In Tournaments all remaining players HAVE to show their holdings in an all-in situation when the betting is over.
2) Is a player allowed to flip one or both of his cards during the hand (no players all-in, for example flop is dealt and first to act bets 3 BB and shows an ace to match one on the flop in an attempt to scare players out...)
No, unless there are no more than 2 players remaining or it's winner-take-all. See next answer.
3) Can a player verbally declare things to 'psyche' other players? For example, flop is dealt and he says 'oh, that gives me a nut flush!'
That's tricky. He may declare things that are unspecific. 'I have a good hand' might still be ok. 'I have the nut flush' is not. It might also be ok to be specific but lying about one's holdings. Overall I think it should be discouraged. I'm very interested in what the more experienced say on this topic. See quote from Robert's rules:
Showing cards from a live hand during the action injures the rights of other players still competing in an event, who wish
to see contestants eliminated. A player in a multihanded pot may not show any cards during a deal. Heads-up, a player
may not show any cards unless the event has only two remaining players, or is winner-take-all. If a player deliberately
shows a card, the player may be penalized (but his hand will not be ruled dead). Verbally stating one’s hand during the
play may be penalized.
4) At Showdown, 3 players in: Player 'A' bets 300, the other two fold, Player 'A' mucks but says 'glad you folded because I only had a 2 & 5 off-suit'
Hand is over, so it's perfectly ok.
5) Are players who folded pre-flop or are already out of the tourney and are still watching and see the street allowed to say things like 'oh, some-one must have the flush...' or 'oh, look at that, could be a full house or two...' or is this discouraged or prohibited whilst betting can still happen?
One player to a hand, so it's prohibited. Railbirds should be asked to stop or go away, players still in the tourney may be penalized.
By participating in a tournament, you agree to abide by the rules and behave in a courteous manner. A violator may be
verbally warned, suspended from play for a specified length of time, or disqualified from the tournament. Chips from a
disqualified participant will be removed from play. Players, whether in the hand or not, may not discuss the hands until the
action is complete. Players are obligated to protect the other players in the tournament at all times. Discussing cards
discarded or hand possibilities is not allowed. A penalty may be given for discussion of hands during the play.
Kicres