Ok to start my Car is as follows:
Mazda Protege 1996 DOHC 1.5L DX

The check engine light has been on for as long as I've owned the car which has been 4 years. I've used the car for 2 years until I got a new car for the family. I have recently decided to bring this car back into commission and would like to get rid of the check engine light.

Things done to the car:
From what I can gather when I went to get the exhaust fixed the guy removed the resonator as it was the piece that broke. He explained to me it wasn't all that nessessary if I didn't mind the louder exhaust. I expressed to him it was ok. So in short there was a resonator delete done on the car. I don't know if this would affect the check engine light as this was done toward the end of my usage of the car when the check engine light was on.

One previous mechanic has told me that the Computer on the car is messed up and required changing. If this is so how do I go about doing this myself. Is it easy enough for me to do without bringing it to a mechanic? Average cost of this part? How do I find the right part? Can I get a used part?

Another mechanic told me that the catalytic converter wasn't ready. I don't know what that meant.

Also my dash lights don't come on and I've been stumped on how to fix it. All the guages and brake lights and such work just not the back light. Any thoughts.

Thanks in advance for any help.

Edit:
One more thing. I am definately looking to change the wheels at some point in the near future. Since my current car has steel rims. I would be lookinng to get alloy. Just wanted to see what my options would be regarding this. IE rim size and tire size. Max upsizing and pros and cons.