Coolant temperature is readily available through the OBDII (OBD2, onboard diagnostics) port that you'd normally use for a scan tool. There are aftermarket gauge clusters (including the HUD unit MarkS mentioned above) that can plug into that port. There are also Bluetooth dongles you can plug into the OBDII port so you can use a phone or a tablet to display data. Same idea.
The Sonic doesn't have an oil pressure sender that'll give you a numeric readout. The car's built-in sensor will only trip if pressure drops below its set point, triggering the idiot light on the dash. To get an oil pressure readout, you'd need to physically install an additional pressure sensor on the engine, which often means using a 't' installed at the stock pressure sender. On the 1.8 engine at least, that's tucked up behind the AC compressor and isn't easy to get to. I don't know about the 1.4 personally, or if there's an alternate place to install a pressure sender.
