In order to test the engine I had to put the clutch housing on, because that's where the starter motor goes. I repaired the fuel pump as well - it just had some dirty contacts. The radiator is leaky, I'll try to get it repaired.
At first the starter motor didn't run but that was because of the thin starter cables I used. When using 10mm² cables it turns the engine but there's no sign of starting yet. Because of the holidays I haven't had much time to look into it further.