The subtitle should have been a clue to the answers I was looking for. Text in blue indicates more advanced material.
1.
2S is weak, showing a 6-card suit and 5-10 HCP. Your options are to bid what you think you can make, or bid 2NT over which partner will show a feature (high card) with a hand in the top half of the range, or bid a new suit which is forcing.
Hint:What will the final contract be? Is there any information that would change that?
Answer: I don't believe there is anything that you could find out that would make you want to play anywhere except 4S. If you could find out that your partner had a singleton club and the DQxx and KQxxxx of spades you might take a shot at 6 but I don't know of anybody below the level of world-class fine tuned partnership that could find that out. So you should bid 4S. But what's the harm in bidding 2NT or 3D?
While 4S likely will buy the contract, your 2NT or 3D bid lets West bid hearts at the three level, and East, who believes 5H is a good sacrifice, bids it now, and you have the choice of getting 300 against 5H doubled or trying 5S which will go down.
2.
Hint: What will the final contract be? Is there any information that would change that?
Answer: It is very likely that you can make 3NT but don't have enough strength to make 5D. But what's the harm in bidding 3D?
Against 1NT P 3NT, West could bid 4S, get doubled, and give up 500 against your game. Or he could pass, East will bid a heart, and you make 3NT.
Once West gets to bid 3S over 3D (
or over any conventional bid you make that shows diamonds), you can no longer make any game, as a spade lead will set either 3NT or 5D. Your best score is doubling 3S for 300, but that's hardly obvious from your hand.
If you really, really, want to show your diamonds, Eddie Kantar has some advice for you. Bid 3NT, and then as you put down your diamonds, say "Partner, I have really beautiful diamonds."
3.
Hint: Does it matter how many aces partner has?
Answer: Partner showed a minimum opening hand with spade support. You have 20 points counting length (
perhaps your ace-rich hand is slightly stronger.) So you should have enough for 6S but partner can't have enough to give you 37 points to bid 7S.
Do you have such a sophisticated relay system that will let you find the SA, HK, and C-KQJx or KQxxx? I assumed Standard American so the answer for this problem should be "no". So you could ask for aces and bid 6S if partner shows none, or bid 6S if partner shows one. (When you bid Blackwood, you are implying that you have enough for slam, so you shouldn't ever bid Blackwood and "chicken out" and stay out of slam missing an ace. Worse is to "chicken out" after much thought and have partner bid six. You'll get the worst of both worlds as either you go down or the director will roll back your making slam to 5S making six.)
Or you could just bid 6S now, since you know that is where you are going to end up.
With three aces in your own hand, and every suit controlled, and about 33 points, you should have no qualms about bidding slam.
What's the harm of bidding Blackwood?
When your partner shows one ace, your opponent has a free shot to double the artificial 5D bid to ask for a diamond lead! A diamond lead will beat 6S, as when West gets in with the CK, E-W will have a diamond to cash.
Note that if you had just bid 6S, West makes the normal lead of the H10, and you have time to set up an extra club winner to discard your D7.
The moral of the story: If you don't need any more information to place the contract, don't ask for it.
I gave you a few examples where unnecessarily playing show and tell will damage your side when the opponents get active. There is another way to lose by making an unnecessary bid when you know where to play: whichever one of you or partner that declares may give extra information to help the opponents defend. Also, there is a slight chance that partner will pass a bid you intend as forcing.
When you need information, by all means, ask for it. But when you don't, just bid your final contract.
I can hear some of the advanced players saying Aha! I can bid Roman Key Card Blackwood (1430) and my partner's answer will be 5C! So I can get away with bidding 4NT!
Of course, I have a hand for you:
Now, partner's "no ace" answer is 5D which gets doubled for a lead, and you've bid both spades and notrump. If you feel clairvoyant and feel partner has the DQ and bid 6C to protect partner's DQ, while you deserve partner to have three clubs, you still pay the piper when East leads ace and another spade.