There's no good reason for trying to make your own OBDII reader. There's a good bit to it. Get an ELM327 compatible reader. I strongly recommend the bluetooth versions, not the serial/USB. You end up with some funny problems, like if there is a difference in ground potential between the computer reading it and the OBDII bus, you can fry the reader.
My bluetooth OBDII reader has been great. I plug it in, or have the driver plug it in, and then I can read data from the passenger seat while we're driving. No wires required, except possibly to charge my laptop, tablet, or phone. They only cost a few bucks on eBay, and despite what you may see some brand name purists say, the generic bluetooth ones work fine.
I lost two name brand serial readers from "mysterious" circumstances (i.e., ground potential difference), at over $30/ea. I've only replaced my cheap bluetooth OBDII reader when I misplaced it. Since I spent about $7 on it, that didn't hurt as much. If it fell under a friend's car seat, I won't care if they keep it.
If you read up on the ELM327 chip , you'll see that it uses 2, 3, or 4 pins from the OBD connector for data. The bluetooth ones also use 2 more pins for power. (block diagram, page 1)
That also gives you all the information you need, if you want to code your own interface (like you would with an Arduino or Raspberry Pi.
Just to answer everything including the original post...
His remote start, door lock, etc, may be possible on some CAN bus vehicles. That's not an OBDII thing. It may be best to do those functions with good old fashion relays. I just finished decomputerizing a 1999 truck (EFI to carb conversion). It's amazing how many miles of wires are no longer necessary, and I still have all the gauges working. :) Actually, they work better than before, which is interesting. Gauges that were jumpy for no good reason are now stable and accurate. I guess there were more than mechanical issues.