Before/After- t-test???

Hello everyone,

Kinda new to this forum. I need help in finishing off this project. So, my research question is whether an increase in the blood alcohol content (i.e., drinking alcohol) lead to a decrease in the mental capacity of performing basic tasks. In order to perform this research (and get a good sample size), I used a software which allowed me to randomly select virtual people who could perform pretty much anything you asked them to. So, I first tested their BAC. Then, I made them take a basic mental arithmetic test, which consisted of 40 questions and could be completed in 4 minutes. I recorded their BACs and their scores on this test. After that, I got them drunk by giving a glass of 250 ml of regular beer and 1 tequila shot. These alcoholic beverages were served in a span of 15 minutes. Then, I recorded their BACs and made them take the same arithmetic test. Following which, I recorded their scores. Thus, I want to compare their test scores before and after getting drunk, which would lead to whether my prediction is true or not.
Let 1 = the score before getting drunk
2 = the score after getting drunk
Null hypothesis: mean1 = mean2
Alternative hypothesis: mean1 > mean2
Significance level = kinda bummed out about this...idk what value to use...
ind out the standard deviation, standard error, degrees of freedom, test statistic, and the P-value associated with the test statistic.perform the matched pair t-test. I am planning on using minitab for this.
also, find out the confidence interval.
reject/accept null hypothesis.
Does this sound right? Or am I missing something??
Also, what would be a good sample size for testing this hypothesis??

Thank you so much for reading this! And for helping me out! :D