in all honesty, it's really not that hard. you basically have it right. it will either work, or it won't. or you'll shock yourself. just use some god-damned common sense, be careful, and you'll be fine. other tips like

run the power wire on one side and the RCA on the other (so you don't get interference)

you want an inline fuse (on the power wire) right next to the battery

you want your ground cable to be pretty short, VERY secure and connected to clean, unpainted metal of the chassis.

ground cable and power cable should be the same gauge.

have fun. here i'm reposting this so it shows up in the thread