help with 97 lexus es 300

Hey, I am attempting to get an after market sound system in my 1997 lexus es 300. What do I need to do to get it done? Will I have to get an after market head unit, but most importantly Can I get an aftermarket head unit? What else would I need to get in order to get a new sound syste, like subs and an amp.

I Just Got A Tune-up On My Car And It Stills Has A Jerking Motion In The First Gearcould It Be The Coil Packs