Search the indicated locations to find all 235 collectibles in the three campaigns (144 observables and 91 breakables).
If you are planning on only playing as a single faction, you can simply purchase all three locked classes for the Knights, Samurai, or Vikings. You can also buy fewer classes and spend some steel on unlocking 'Champion Status' time, which allows to gain bonus XP and other rewards for a limited time. This will allow you to unlock 7 of the 9 classes at the beginning of the game. Complete the Basic and Advanced Tutorial to get 3,500 steel.