1. PAC makes a speaker out to line out adaptor that works really well. Mate this to a Metra radio harness and its PNP.
2. The TRD exhaust gives great growl that is a low rumble, but pricey. Magna flow produces another good setup.
3. Lower your tC. The Celica hasa lower center of gravity. You need a setup like the Hotchkis Stage I TVS that has larger sway bars. OEM strut are fine till they need replacing or you could go with TRD or Tokico. For all out you need 3-way adjusable coil-overs. Add a front strut bar.
4. Maybe, but why? I assume from this
reason here. You will have to run a standalone e-manage and integrate inputs into the Scion ECM. Contact
Jotech Motorsports for this info.