I dont think the height and weight makes any difference.
left and right does matter. For example of you have an MC and your MR gets injured your right footed MC will work better in this position than a left footer.
It also helps on free kicks and corners.
In regards to quality scores, you need to be careful as quality for a can be affected by the entire squad and therefore brought down by lower quality squad players. Ie the first team amy be a lot higher than the average quality suggests.
Also depending on how you load your skill points an average looking striker could have a massive attacking score and very low physical and defensive score.
Take this into account average means AVERAGE across everthing
If captain have some effect I guess the effect is not that substantial.
However, regarding the left or right legged do you think it is that important? You can easily see on the market there are many left foot who is DR, DMR, MR or AMR, vice versa there are many right foot who is DL,DML,ML, and AML. According to you, we should not buy these players since they are in the wrong place with the wrong foot?
I think the foot is important in every position for determining the winning solution for the game engine. Why have it if it is not important. Height and weight might have some influence, but probably very little. tall defenders might be better, heavier players might be better or worse depending on the position. If not, then the height and weight are there to make things a bit more human.
When can we get confirmation of any of these questions?
I think it gives a small performance boost to a player; at least from my perspective. My striker I had since League 1 has been scoring goal after goal after goal. And he's only two stars.