Rotors are like shocks and struts. You should always replace them in pairs. Its an issue of even handling and even brake pressure.
I'll let you off the hook for the wiring thing, but just so you know, you would have no risk of fire, the wiring that is in there is heavy enough it shouldnt burn, unless you have bad contact at a splice and thats where you would build up heat and possibly have failures for the wiring. However a dead short on those wires would pop fuses long before the wires burn. The fuses are designed to blow before the stock size wiring could burn, so wires that heavy you wouldnt have a problem. how did you find out your rear end was a 4.10? Really if the guy rebuilt the rearend he probably knew which one he had. personally on a 5.0 I would prefer the 3.73, especially if you are modding for power, you arent gonna hook up well with that 4.10 and your first shift comes way early. Back to that intake, that is definately a 5.0 HO intake, the GT40 intakes plaque is way different. There isnt a lot of difference between the two intakes so the HO is fine, especially if you are on a budget. Who installed that e303? If you did not personally install it and it was in when you bought it, then I would say there is a high likelihood that whoever sold it to you was not completely honest or you misunderstood them. An E cam is a pretty agressive cam and I would expect you to be pinging unless you are running premium during the hot months. Im sure you are fine during the winter.... But yeah.
IDK why you would want that cam anyways with stock heads, unless you went with larger bore valves.
