Is Romans 14 Saying That Christians Can Just Make up Their Own Rules?

Questions about whether the Christian liberty described in Romans 14 is the same thing as making up our own rules, weaker and stronger Christians in Romans 14 and 1 Corinthians 8, and the claim that once a person accepts Jesus as Savior, he is redeemed and no longer a sinner.

• How can we explain the idea of Christian liberty as found in Romans 14 to someone who claims it’s just the same thing as making up our own rules?
• Regarding the “weaker” and “stronger” Christians Paul talks about in Romans 14 and 1 Corinthians 8, should weaker Christians eventually mature in their faith and understanding, and is it the stronger’s job to help correct the weaker’s theology?
• How should I respond to the claim that once a person accepts Jesus as Savior, he has been redeemed and is no longer a sinner?