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.