@mathis said:
The high a' near the end sounds louder recorded than played back and since I'm currently learning my first lessons about choir I wonder if this high a' is a good idea anyway in a soft context? Can anybody elaborate who has some more significant choir experience?
no, your intuition is right. the group just isn't getting it done up high yet. a soft a is tricky but perfectly fine with a good choir. but most singers can't manage it at any dynamic/vowel (although they'll all insist they can) so it might best be considered the beginning of a "professional" range that can continue up to c (allegri miserere for example).