what size megafuse?

First off we need we need to clarify the intended purpose of the fuses in a circuit.
Fuses are there to protect the wiring in case of a short not the "components" in that circuit.
That is why you want the fuse to be close to the power source. If you put the fuse close to the component and have a long wire run between it and the power source and you have a short somewhere between the fuse and the "battery" that wire is going to fry its whole length. The fuse as stated earlier is sized for the wire it is protecting or for the max "draw" in that circuit which ever is the lesser amount.