Replacing Shaker 500 Help Plz

I bought a 2005 v6 mustang this march and have had problems with the shaker 500. I don't listen to the radio and it doesn't have an aux port so I make cds and play those everywhere I go but they often skip. I read this is a common problem and I want to get the stereo replaced. I literally know absolutely nothing about cars so bare with my cluelessness please. I want to get a Power Acoustik PD-342
(https://www.ebay.com/itm/181669295122) . From my understanding I will need to also purchase a metra 70-5521 amplifier wiring harness and a metra AFDI-5V 12v to 5v converter as well as the dash kit. Can anyone verify if this information is in fact correct? Is there anything else I need or will have to do? I'm having someone else install it but I want to make sure I have all the required parts just in case they might not know. Also what is the process like replacing the speakers? I don't care about bass (I have it all the way down). I just like my music loud, crisp and clear. Is it worth replacing the speakers too or should the factory speakers be fine? Also if I do replace speakers is it any easier to replace them at the same time as the stereo or will it be okay replacing the stereo only and seeing how that goes? Please provide me any and all information you can in regards to replacing the shaker 500 stereo and possibly speakers. Thank you in advance