I guess by "the park" you mean Magic Kingdom.
1. 7:45-7:50-ish for WDW Resort guests.
2. Nope. Not on AM EMH mornings.
3. Yes. At about 5 minutes before the "REGULAR Hours" opening time.
So, this coming Saturday, the Welcome Show would start about 8:55AM.
If you are in Fantasyland or Tomorrowland for AM EMH and you want to see the Welcome Show, you'd have to come back to the Hub and stand in front of the castle.