Arduino + OBDII(VPW only) > 20x4 LCD display

Im working on a standalone OBDII scanner and display for my car using an Arduino Uno. The car is a 1999 Pontiac Trans Am which uses the VPW protocol so ill be using an OBD VPW to RS232 interpreter chip. I think ill be powering the Arduino off the 8v off the 78L08 voltage regulator and tie arduino ground to chassis ground.

My questions are: Are there any major software problems I may run in to? Do I have enough power and signal isolation to protect the arduino (and my cars ECU)? (Do I need an opto-isolator or something?) Any other foreseeable problems? Thanks

Optoisolator wont hurt, you will need a regulator if you arent using the onboard regulator on the arduino.

Can u post the code, here? tks :D

I have build an almost identical design except that I am using the ELM327. I am also very interested in the code.