Hah, glad to hear that enthusiasm! Yes, the Grundregelwerk is free as a pdf. Uhrwerkverlag has the rest, don’t use Amazon or other resellers. To play I highly recommend Mondstahlklingen (Weapons, Armour, Equipment and Crafting - which is a really cool system) and Die Magie (Magic, duh). I’ll check which of the other books I use regularly once I get home. There are tons of regionalia (Zhoujiang is my favourite, it adds china made-in-china) as well as Die Welt (which gives a nice overview).