Existential Comics has suggestions
for amateur philosophers.
Being and Time, Martin Heidegger.
Difficulty level: hard
Who to read first: Kant, Hegel
Heidegger was one of those philosophers who thought everyone before him was horribly off-track. In theory, Heidegger can be read on his own, as he was often starting from scratch, but he was very influenced by Hegel, Kant, and Kierkegaard, and his works are again, long and difficult. Unless you are very interested in him, just get an overview instead. If you do want to dive in anyway, you should listen to Hubert Dreyfus lectures first.