My POV

1)Which special ability do you think its best for strikers?
Good to have, but not necessary, I'd take Pen Specialist over One-on-One. I noticed that One-on-One only works effectively in matches when he dribbles past players and takes the shot himself. If he receives a pass from someone, he'll miss.

2)Teaching new position has a good influence on performance? If so, which one contributes more amc or wingers?Anyone tried?
Wingers. I believe AMCs are better not having dual roles. It is also believed that while training, assuming you assign cones each time you get them, their performance will drop slightly. So I usually collect 50 cones then assign the cones one shot.

3)Is that really important to being able to use both feet?
I believe so, especially for strikers and midfielders

4)How those hall of fame top scorer stats are allocated? How much diffenrence is ok between attack and defence and physical?
My take is Attack - X, P&M - X-5, Defence - X-20 (difference between to stats is not supposed to be more than 20)