2002 Protege 2.0L Check Engine Light w/3 Error Codes. Which to tackle first?

My girlfriends 02 Protege had the check engine light come on, so I checked the codes.
Car has about 150,000 miles on it, had a blow out at speed on the highway, new tire and oil change about 2 weeks ago. I've found some pretty specific info on the forums but, and found downloads of the manuals/wiring diagrams, just want to make sure I'm on the right track.
Which of these needs to get done first, and do I need any specialized tools?
I got the following codes:
PO550 - Power Steering Pressure Sensor Switch/Circuit (Changing power steering fluid seemed to solve this problem in one forum?)
PO401 Exhaust Gas Insufficient Recirculation Flow (Clean or replace EGR?)
P1250 Pressure Reg Control Open Shorted (Replace solenoid?)
Thanks for your help. I'm becoming more confident but, still used to having someone look over my shoulder when I work on the car.
 
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