Yes. This has recently been announced.
Most likely, yes. Synopses have been released for all episodes in season 4 other than the final two which, based on episode 24 being the Equestria games, will probably be a two part finale. No episode between now and then will center on Twilight, so that puts the finale as the time when Twilight will likely get her key.
Episode #232, Season 7, The Fighters, original air date: April 24, 1966.
Neither Apple Bloom, Scootaloo, nor Sweetie Belle get their cutie marks in this episode.
Episode 3 season 1
The episode with all the little people is the aptly titled season 5 episode 'All The Little People'.
When the cows come home
Probably not. It has been said by the production team of Equestria Girls that Equestria Girls was meant to be a standalone, and not be connected to the TV show My Little Pony: Friendship is Magic.
The Equestria Games arc of My Little Pony seems somewhat similar to the Grand Galloping Gala arc of season 1. So it is logical to conclude that it will be right before or part of the season finale.
yes
No. It has been stated that season 6 will focus on exploring Equestria.
Season 1, Episode 1: Friendship is Magic
No. It is the last episode of season 3, but there will be a season 4.
It is not known. The only information known about season 5 is that it will have 26 episodes.
This episode has already been released.
Probably. Since the box was introduced in the pilot and the Mane 6 finding their keys has been a story arc for the season, it will likely be concluded as part of what appears to be a two-part finale, as episode 24 will involve the Equestria Games.
Photo Finish is in season 1 episode 20 "Green isn't Your Color"
No. It was the last episode of season 3, but season 4 started up on Nov. 23rd, 2013