Lots of good questions, I have tried to break my answer up by the questions you asked.
How do we know that the things in the Bible haven’t been messed with?
We know that the Bible has not been messed with because when we write our English Bibles it is always written by looking at all the manuscripts (old pieces of paper with the Bible written on them) we have of the Bible and we have 1000’s. We keep on finding older and older versions of the manuscripts and they agree with what we have currently. Some of the manuscripts date back to within 100 years of when they were written. There is better evidence for the accuracy of the bible than for many historical texts we take for granted.
Where there may be differences between the manuscripts, a Bible written for English speakers footnotes the issues so that anyone can know what discrepancies there may be. These discrepancies are usually in the spelling of names or of hard words to translate. In general (at least 99% of the time) it makes no difference to what the meaning of the text is. So I can say with great confidence we know that the Bible has not been messed with.
I know that God treats everyone the same so there’s no way that he looks down on women…so then why isn’t any of Jesus’ disciples women?
Good question. Firstly some of Jesus’ disciples where women, Mary Magdalene was one. But I am guessing what you meant is ‘Apostle’ the name given the twelve special disciples Jesus has.
Jesus did not choose women to be his apostles not because they were not fit or able but because this was not the role he chose for them.
The bible sees men and women as being equal in status and value but dufferentiated in roles. This is the teaching in Genesis - everyone is equal but not everyone is the same. Its an important idea to grasp so have a look at - Gender.
The chief role for men is leadership or as Jesus puts it slavery. Huh! Sounds strange right! God’s idea of leadership means being a slave. Jesus only chose men as apostles as their roles was to be slave for Jesus, the chief slaves of all the Christians. Have a read of Mark chapter 10 verse 35 - 45 you will see that Jesus see leadership as slavery. The apostles where all men because their role was to be a servant (or slave) to the church for the sake of Jesus. When you start thinking about it this way being an apostle is not the cool job it sounds like at first! All these men died as a consequence of what they believed.
The greatest example of what it means to be a man is Jesus. Who, even though he was God, made himself a man to be a servant! When Jesus died on the cross he did so as a suffering servant (read Isaiah 52:15 - 53:12 it all about Jesus as a suffering servant). His death was to pay for yours and mine rebellion against God. If this is not being a true servant I do not what is!
If a woman was chosen to be a disciple then wouldn’t it be more convincing to those people of his time that God had the power to do anything?
Jesus did act differently to women and children in such a way that the leaders of Israel where insulted. Jesus spoke to women, children, tax collectors (basically thieves working for the government) and prostitutes. This showed he had the power to forgive anyone. The act that showed that Jesus has the power to do anything is his resurrection. After Jesus died on the cross he came back to life not as a ghost but to live forever with a real body in heaven with God. Read Matthew 28:16-20, you will see that all power and authority s given to Jesus because he died on the cross at his Father’s request. It this act that sets Jesus apart from any other person in history!
In summary Jesus did not chose women to be apostles because it is men who have the task of serving or being a slave for the church. So if a man is leading in a church he should be a slave to all the people he serves otherwise God will not see him as a good leader.