Honestly, the best place to start is the Book of Concord. This is the foundation document of any confessional Lutheran church. This book includes the Augsburg Confession, Luther's Large Catechism, etc. and explains in detail the Lutheran positions on many subjects. As it is an early document (for Lutherans) there has been some theological development over time, but it is still a perfect place to start.
Topics to consider....are you thinking more social, theological, etc.? The Lutheran church has a rich tradition of Theological thinking, so there is a lot of content on that end. Aside from that, the different Lutheran bodies hold different positions on social positions, and that affects their theology as well. Also, some Lutheran church are episcopal in polity, while some are congregational, or a mix. Then there is the question of churchmanship, some are high church, some low, most in the middle - but generalities can be made depending on the group (LCMS, WELS, ELCA, etc.).
Not a lot. A list of churches they have a Altar and Pulpit fellowship with can be found here:
LCMS Partner Church Bodies - The Lutheran Church—Missouri Synod
I do not see a presence in Paris, but they are in fellowship with the Evangelical Lutheran Church of England. They have two parishes in London:
Congregations