Forget the OEM stereo. It's a quality unit, but Japanese radios use a different frequency range than we do, so the radio will be all but useless to you. I stuck a cheap Sony head unit in there for the time being. Eventually, I'll replace it with a big double-DIN unit with a backup camera. Some people are all about authenticity, though.
Swapping out the stereo is easy, but there are some things you have to be prepared for ahead of time. You're going to need an adapter to match the new stereo output to the vehicle's wiring. They're easy to find. All Toyotas of that model year can use the same adapter. I got mine on Amazon.
You said you have the CD and tape deck, right? Is your stereo comprised of two stacked components? If so, here's where it can get tricky. There are actually two different stereo connectors in your dash. They're in parallel and they both do the same thing, but the connectors are different. Your current stereo is plugged in to one, but you want the other one for your new head unit. You may need to dig around a little to find it. You'll know you have the right connector when it matches the one on your adapter. Once you find the right connector, the rest of the installation should go by the book.
What else could go wrong? Some models have a factory amplifier located behind the panel over the left wheel well. If you install the new head unit and can't get any sound out of the speakers (or if it cuts in and out like mine did), you're going to have to bypass or replace the factory amplifier with your own. I've got some tips for that too, if it comes to that.
Good luck.
