Regarding Medium:

If there are multiple Mediums in play and they all have counters on them, do their individual R&D accesses apply?

Example: 2 Medium with 2 counters each = 4 additional cards accessed?

Regarding Imp:

If there are multiple Imps in play, can each Imp trash a card per turn?

Thanks in advance.

Yes, each medium adds its numbers to the draw. But the base draw is still one. Two 2v Mediums will each add 1 card accessed.

Each Imp's limitation applies only to itself.