Coming from experience...

Anything you build is going to be harder than you think it will be to do.

Coming from a computer hardware background, I can tell you that real time display without so much lag that it becomes useless, while still doing the conversions needed to turn your raw voltage data into what you want to know, is a milestone in itself.

Data logging is a can of worms that companies with plenty of money to invest for years before getting any return on.

Now, assuming that doesn't scare you off. ALL you need to do for the fuel guage percentage stuff is to know your empty and full fuel gauge sender voltages and calculate the percentages accordingly, since the sender is just a linear potentiometer. But, if you want to get real accurate, you have to do some experimentation to find out what the voltage values are for known amounts of fuel from empty until full, because most tanks are not the same dimensions from top to bottom.

For the air intake sensor, you need to figure out what voltages correspond with what temperatures as well.

For fuel mixture, you need a wideband O2 sensor, because the stock O2 sensors don't have a fast/stable enough render time and signal resolution to give you anything useful otherwise.

To top it all off, data logging systems, and Dash race clusters are becoming more affordable, and commercially available.

If you want to do it as a hobby, I say go for it, but plan on it being a very involved and lengthy project that might last longer than you own your car.