2001 Pontiac Montana All sensors bad?

I took my van (that is eating gas and accelerating poorly) to autozone and hooked the computer up to it. It's a 2001 Pontiac Montana, the codes read:
Spark plugs & wires
Bad throttle position sensor
Bad mass air flow sensor
Bad oxygen sensor (both)
Bad coolant temperature sensor

Now I don't know much about cars. But financially speaking I was able to get the plugs and wires today. I also checked my gas cap and purchased a new one, in hopes that's the true cause of at least one of the oxygen sensor problem (the rubber was completely gone on the old gas cap). Now I don't know where to begin on the rest of it. Could there be an overall cause to the sensor problems? It's hard for me to believe they all are broken at the same time. Is there a fuse or something else I should be checking before putting A LOT of money into new sensors? Someone please help. Thanks in advance. ~Kirsten