The two RCA jacks are most likely for the back up camera itself, the yellow one is for sure. The blue may be for a Mic or something. Locating the the reverse gear wire is very easy. Just look on your steering column near the firewall, there are two wires coming off a switch that run UP the steering column, the one you are looking for is Green. The parking light wire is a ground switched circuit, so you can just put an eyelet on that wire and ground it to bypass it.
As for your speaker connections, it looks as if your missing a plug in connector pigtail for the back of the radio. If that is the case, you can most likely get a new one through the manufacture or you may be able to snag one on eBay. The two small 18 gauge blue wires on coming out the back of the radio are most likely for a power antenna trigger, and a amp signal trigger if your wondering on those!