i've fixed many Best Buy installs. but someone with zero experience will struggle with even the simplest of tasks. if you're a good mechanic and are comfortable taking a car apart, have general electrical experience working with wiring and have the tools to make wiring connections (wire crimper, stripper, electrical tape, wiring, soldering iron, drills, screwdrivers, zip ties, split loom, assorted hardware, etc.) then it's a doable task. even getting through the firewall can be a substantial challenge for a newbie.
if you buy a complete amplifier installation kit you generally get everything you need from a wiring/hardware standpoint. you'll need some extra speaker wires as well. intercepting speaker wiring behind the HU is easier than running through the doors.
you can let Best Buy do the install, then go over it in detail, share pics, and we can let you know if they did something silly. if you have local car audio shops, talk to them as well.
at a minimum, you must be good with your hands, have necessary tools, and have a place you can work on the car. if the answer to any of those three is no, then pay someone.