It doesn’t really matter in a tiny house whether you start at the breaker box or end there. I had read somewhere to leave 4′ of extra cable for each circuit to wire the breaker box. I think that is probably excessive in a tiny house but do leave plenty extra. Before starting a circuit, make sure you know what gauge wire that circuit needs. Since the knock-out holes going into the breaker box have sharp edges, you’ll need to get inserts that snap or screw in to protect the cable from being cut. As I mentioned, I had an electrician wire the breaker box and add the power inlet after I had wired the circuits.