These are some great questions you've got!
First of all, ideally, yes being a Christian means you will go to Heaven. However, the discrepancy exists where people claim to be Christians, but don't live as followers of Christ should. A Christian is someone who has devoted their life to following God. We believe that Jesus is God in the flesh and that he died for our sins. The Bible says that by believing Jesus died for us, and that he is the Way, the Truth, the Life, and the only way to the Father, then we will be blessed with eternal life with Him. That is the definition of a Christian, and it is how Christians should live. Obviously we are not perfect, no one is. But we repent when we sin, praying for forgiveness, and seek guidance from the Lord to be stronger in Him and live as we should. Many people today believe that simply going to church makes them Christian, or saying they believe in God makes them Christian. In reality, they are lying to themselves because one is only a true Christian when they know Jesus as the Way, the Truth, and the Life, and seek to live well with the Holy Spirit. So, overall, yes, Christians go to Heaven because we follow Him and how He wants us to live. Sadly, it has become an epidemic today of people claiming to be Christians when they don't live like God wants them to.
Next, there is much wonder over what Heaven really is. Truly, what I believe from what the Bible says, is Heaven is God's domain. There is where we will finally experience His glory to the fullest. It is eternal, where our weary souls are fulfilled in the presence of the Lord. It's in the Bible that the streets are laid with gold, and everyone there appears as they did in the prime of their lives. It is perfect, holy, and eternal.
Martyrdom is also an interesting topic that I've thought of myself. I can't imagine how being killed for your Christian faith can be considered a "bad" thing in the eyes of God (obviously we are human and can only go based on what we learn from the Bible). Many disciples in history became martyrs for their beliefs, because they were killed for spreading the good news of Jesus. Paul is an example. Obviously I don't think it should be a goal for Christians to go and die just to be martyrs; that's wrong, the Bible doesn't say to do that. Just remember to always stand strong and steadfast in your faith and Christ. Then, you will walk the path that God laid out for you.
"Jesus paid it all
All to Him I owe
Sin had left a crimson stain
He washed it white as snow"
Regarding believing in God for a happy life, the Bible doesn't say that is always the case. The Bible says that in the world, the wicked will prosper, but as Christians we should not be tempted to turn to those wicked ways. The great shall become the least and the least shall become great. We are not of this world, and our true prosperity awaits being with Christ forever in Heaven. Refer to Jeremiah 29:11 "'I know the plans I have for you' declares the LORD, 'Plans for prosperity and not for calamity to give you a future and a hope.'" God has a plan for everyone, and if you hold close to Him, then your life will fall into place as it should according to Him.
Finally, church. Praying and asking for guidance and forgiveness is incredibly important, but we should never forget how important it is to WORSHIP God and study His Word. Church provides a place where people can gather together to do these things (as the Bible says it is good when people come together to worship the Lord). Unity and brotherhood are so important in Christianity and going to church really is the ultimate output for that. It's a place entirely dedicated to Christ. When people gather there to study, pray, and worship, it is truly a beautiful thing and is vital. Everyone has their own personal relationship with Jesus, which very often is addressed during alone time. Church is important and as Christians it is important that we go to come together and give thanks to God. However, if God is calling you to stay home on a Sunday and work some things out with Him alone, then do that. Everyone needs alone time to get right with God. I'll admit that I've been struggling with pornography, and I am incredibly ashamed. But very often I'll pray for ten to twenty minutes alone for the strength to keep fighting and for the guidance of what steps to take. I do that because it's part of my personal relationship with God and I address it in private prayer. But, it is also important that I find people I can trust, my brothers and sisters in Christ, to hold me accountable and help me in this battle. That is the importance of going to church: helping each other and being there for each other on everyone's spiritual journey.
Responding to your message was awesome, and I can't wait to hear what you have to say! I've never openly admitted my struggle with pornography before either, so thank you. I believe that God was using you to help me take that next step I needed to take.