Welcome to the CAC, "teddybenz22".
I think it unlikely that the the previous owner's nitrous oxide system is causing problems with the door control modules, but the easiest way to find out is to remove what's left of the nitrous hardware.
There are a variety of different ways to add nitrous to a C5 but. generally, the electrical part using takes this form...
There is a "master switch" or "master button" which turns the power on and off. It will have one wire going to a source that his hot with the key on and another wire going to a device which connects to the ETC harness and provides a wide open throttle signal. These devices are sometimes called (WOT boxes). The wide open throttle output from the WOT box connects to a relay and then to ground. Battery voltage is connected to the load side relay and then to the solenoid(s) and the other side of the solenoid(s) are grounded. When the master switch is on and the WOT box sees a WOT signal from the ETC, power is fed to the relay and the relay energizes the nitrous oxide solenoids. But...I digress.
It's possible the remaining parts of the nitrous oxide system were poorly installed and are affecting the door control modules. I'd disable that switch or button by finding where it connects to a hot-with-key-on source and disconnect it. Then road test the car to see if the door-related codes come back.
As for the fault codes you are seeing--
B2252 is a problem with the driver side door lock position sensing, likely a short to ground.
B2265-65 are problems with the sideview mirror position sensors detecting over or under voltage.
B2282-85 are problems with power feeds to the door modules
U1064 is loss of communication with the BCM.
If you want to DIY the repair, you first need a set of 2001 Factory Service Manuals. Then you need to follow the diagnostic instructions for all those B codes.
If you're one of the folks who doesn't feel the need for an FSM, the job may be more difficult. First step is to inspect the battery and the charging system. Any problems with the battery or alternator or charge system wiring might cause a problem with the door modules.
Then, I'd suggest inspecting all connections between the door modules and the car's wiring harness. Be looking for shorts to ground as well as bad connections. Check connections at the door locks and the harnesses which go to the side view mirrors. I'd inspect all grounding connections to the door modules, the locks or the mirrors. Correct any problems you find then road test to see if the codes return.
Lastly, you will need to disassemble the doors to access those modules and wiring.
Good luck.
