#1
If i play chords like Amaj7 Dmaj7 A7 D7, what key of the pentatonic scale do I play in for soloing.
#3
D major pentatonic

Remember, just because a progression starts with a particular chord does not mean it's in that chord. Check for I-V movements and use your ear and check if it resolves anywhere.
        ,
        |\
[U]        | |                     [/U]
[U]        |/     .-.              [/U]
[U]       /|_     `-’       |      [/U]
[U]      //| \      |       |      [/U]
[U]     | \|_ |     |     .-|      [/U]
      *-|-*    (_)     `-’
        |
        L.