reefer guy,
all credit shd be given to yazid who helped me with the internal wiring.
i'm actually quite nuts and scared to do electrical stuff until i get my hands dirty! it's rather easy actually.
ervine,
the contactor is to prolong the life-span of your expensive EH011. cos the live wires from the MCBs could be really hot. another point from yazid.
box wise, just get the one the shop recoemmends. i remember it's only a couple of dollars.