P0154, P0300, P0550, P1133, P1153

[Rora_in_kc]

We just bought our 1996 Rora from auction (Awesome buy). Found the recall for the fuel rail and lines. Had the local GM dealer replace since it was never done. Service Engine light is always on, sometimes flashes and chimes. Had the service department pull the codes and these are it. We have just finished replacing front and rear brakes. Bought new plugs and wires (AC Delco), need to do radiator flush, power steering flush, and transmission flush (has too much fluid?). So, here are my questions.
1)My hubby drained the radiator, but cannot figure out where to put fluid back in. Dealer says use the overflow, but just sits there, doesn't drain into radiator. Missing something?
2)P0550 power steering pressure switch circuit low voltage. Will power steering flush eleviate or is there something else we should be doing?
3)P0300 engine misfire... plugs and wires... in process.
4) P1133 & P1153 - o2 sensors. I have read where all four are located. How do I check to see if they are working properly?
5)P0154 Hols circuit insuffiecient activity bank 2 senor 1
6) radio is gone and causing codes - they took out the radio and the CD changer in the trunk.
7)B1081,B1092,B1037,B1080,B1073,B1074,B1093 stored in IPC - no info given from dealer.
8)Took in to Cottman Transmission for free tranny check because she is slow to engage, was told by them the MLP?? Dealer doesn't know what that is. Any insight or blowing smoke up my you know what?

I know this sounds like a lot, but she is still a wonderful buy. All in all, when you have tuned out the chimes, she runs great! Has the autobahn package. Someone really loved her when they bought her, but she has been abused as of late. Should be a black car, but has the green hood and trunk lid. We really want to get her back to her glory. This is my hubby's play car. Even with everything, she is still a great car!

Any and all help greatly appreciated.

J & K