4. Carry more health shards/stimpacks
I think three is enough. Any more and things would be too easy.
5. Predator's throwing disc should do more damage
But it's almost always a one hit kill. How much more damage do you need?
6. Alien's heavy attack should do more damage
This I agree with. The Alien's heavy attack feels weak to me, and it seems to have very short range compared to the Predator's.