Curious about Islam - looking for some clear, friendly answers, assalamu alaykum

Assalamu alaykum - I'm coming from a Western background and have a lot of questions about Islam. I'm thinking about whether to embrace it and would appreciate straightforward explanations. 1. What makes someone a Muslim? From what I understand, a person becomes Muslim by sincerely declaring the shahada - saying there is no god but Allah and Muhammad is His messenger - and meaning it in their heart. Is there anything else needed besides belief and that declaration? 2. Which books are accepted as Scripture? Which texts do Muslims consider to be the word of God or reliable guidance? I know the Qur'an is central, but what about other writings or sayings attributed to the Prophet - how are those viewed? 3. What happens after death and is it the same for men and women? How does the afterlife work according to Islam? How does someone attain Paradise or otherwise? I've heard mixed things about gender and treatment in the afterlife, so I want accurate info about whether men and women are treated equally in the sight of Allah. 4. Who is considered an enemy and how should people be treated? What does Islam teach about enemies or people you disagree with? How are Muslims instructed to treat others, including those who oppose them? 5. What's the difference between Sunni and Shia - are those the two main groups? I've seen those terms a lot. What are the basic differences, and are those the primary branches of Islam? 6. Who was Muhammad? Who was the Prophet Muhammad in Islamic belief and why is he important? Thanks in advance for clear, simple answers. I'm trying to learn without assumptions and want to make an informed choice. Jazakum Allahu khair.