problem with setting up a new audio system?

my old amp is toast. With that being said i want to go ahead and get a new set up in my car new car speakers subs and tweeters and of course a new amp. Now the problem I'm running into is if the factory amp no longer works then that means i either need to connect the car speakers to the amp that powers the subs or i need to buy separate amp for the car speakers. I'm new to this so i don't know. Another problem is do i just keep the old amp plugged in or do i remove it or what would it be a issue? i have the car listed above LE model. i planning on putting an aftermarket single din radio in.