Great. 2 people answered and they disagree on everything except the secret chamber q. 
.
Just for the record my guess for q1 is A2.
Q2 and small Q2 I'm uncertain (I could see either way).
I'm wondering if there any concrete rulings on these (would love links if you've got them) or if these are just your gut opinions.
There are lots of concrete rulings by Donald, in threads such as these. He has ruled on all these things before though. (And some of these questions, such as effects in turn order starting with the current player, is actually stated in the rulebooks, as Ingix quoted.) You might find the rules document I made helpful, link in my sig. It includes all the timing rules.
Something that is implied in this thread, but not explicitly stated, is an addendum to the rule about several abilities that trigger at the same time. As stated, each ability is resolved by the player it affects (and then ordered by that player if s/he has several). The addendum is about an ability such as Embassy's Silver gaining, that says
"each other player". This ability is resolved
by the player it addresses, so the player gaining Embassy in this case. That's why, in Ingix's example, the player gaining Embassy decides the order of
"you may exchange it for a Changeling" and
"each other player gains a Silver". (When s/he chooses
"each other player gains a Silver", this of couse creates a "gain a Silver" effect for each other player, which is resolved by each player in turn.)
Another thing, that I don't think is part of any of your questions, but which Donald addressed, is that an ability can cause another ability to be triggered without actually triggering it. In all the examples with Ambassador, Embassy, Changeling and Eavesdropper, a new ability was triggered directly from the resolution of an ability. In those cases, the new ability interrupts that resolution, as has been explained. But resolving an ability (which was triggered by some "event") can
change conditions in the game so that another ability is actually triggered from the same "event" that triggered the first ability. In that case, the two abilities are "happening at the same time". The new ability is added to the pool of abilities that are triggered from the same "event" and waiting to be resolved. (There could be several.) First you finish resolving the current ability. Then you decide which of the pending abilities to resolve next, etc.
Donald's example of start-of-turn abilities with Hireling is a perfect example. The "event" is here "start of turn". Another classic example is Moat and Diplomat/Secret Chamber. Another player playing an attack is the "event", which triggers your Diplomat. Resolving the Diplomat causes the Moat to enter your hand. The Moat reaction is now added to all the possible abilities you could resolve from this "event" (along with reacting with the same Diplomat again if you kept it in your hand).
(I prefer calling things that trigger "abilities". An ability can consist of several effects. "Each other player gains a Silver" is a triggered ability. When you resolve it, a Silver gaining effect happens for each player in turn order. Each of those effects could trigger other abilities. This is also important because once you start resolving an ability, you always finish resolving all of its effects.)
)