I missed this lab and got info from a friend but none of it is making sense, ANY help would be awesome

My percent errors are all 25%+, one even got up to 147% o_o
I asked my teacher about it, she said that the we didn't really use atwood machines and the whole lab was going to be off.

So in my post lab I made a graph of experimental acceleration vs. mass difference.

I have answers for the questions I just don't know if they're right.

Q1) How do you find (g) from the graph? -Could you just divide (a) by (mass difference) which is the slope of the graph. Because of the equation a=(m2-m1)g

Q2) How does the fact that the string has mass affect the lab? Is it important? -I don't know how it affects the lab, but i'm guessing it's not important

QUESTION 3)Compare the magnitude of the force of friction to the other forces present in the experiment. Is friction a significant factor? -The only friction is the string & pulley, right? My teacher told us to assume it's a frictionless pulley, so I have no idea

QUESTION 4) When the net force remains constant but the total mass increases, what happens to the acceleration? -according to my theoretical acceleration results, when our total mass increases the acceleration decreases.

QUESTION 5) When the total mass remains constant but the net force increases, what happens to the acceleration? -according to my theoretical acceleration results, when our net force increases the acceleration increases.

QUESTION 6) Explain specifically whether the answers to the previous two questions reflect Newton's Second Law -Q5 reflects it because the a change in net force causes acceleration. Q4 i'm not sure how it reflects the second law.