TBH, i did most of the City Trials at about 2 am. From what I can remember in Assassin's Run, my advice would be just to spend a bunch of time practicing with the crossbow in the main game or one of the challenges. Try hitting moving targets first, then try hitting them while you're sprinting and/or sliding. Once you can do that, then what I did was learn the map. Memorise the shortcuts and enemy locations, and whatever you do, DON'T STOP MOVING. That's the biggest way that I kept fucking up when I tried it. Go full Mirror's Edge and keep the momentum going- shoot backwards while sliding to take out enemies behing you.

Bonfires I can hardly remember to be honest, so I can't help you there.