Like a child lost in the woods...

I just recently repaired "layers" of CEL codes on my 2008, but mine were related to misfires and a bad coolant valve. So your problem might be 2-3 different things, what I did was try to start with something easy. Have you tried cleaning the MAF sensor yet, using the proper cleaner and a Q-tip to gently clean?

 

welcome!

if you are going to diy, start by setting up tech stream with mini vci. you can find info searching google and clicking on threads here.

auto parts stores don't always read the multiple prius ecu's correctly.

then post the codes again if different, and consider a service manual purchase. 150k is nothing on a 2004, so you want to get it in tip top shape and maintain it well.
do you know anything about the service history? you can get dealer info at toyota.com/owners, along with a maintenance schedule.
there's a major service at 120k, so you want to make sure those things were done.

if your missing the speedo, that's a capicitor on the board that needs resoldering, or you can do a rebuilt from texas hybrid batteries.
the radio may be a fuse or wiring issue, but if it's dead, check salvage and ebay.

all the best!

 

I think there are only three codes on that list that can even be found in a Gen 2 Prius repair manual, which leads me to second bisco's suggestion about getting the codes read another way.

I really don't have an explanation for how the parts store scan tool came up with those other codes. Generic tools are sometimes missing descriptions of Prius-specific codes, and we've seen at least one phone app that sometimes decoded the first nybble of a code wrong, and displayed codes with the first two characters off. Just coming up with extra codes out of the aether ought to be harder. Maybe the reader was used recently on some other car? Hard to say.

 

Those Yellow Top Optima batteries are junk. I bet if you load tested that 12v you'd find that's the source of all your problems.

 

+1 to cleaning the MAF and also cleaning the throttle plate and throttle body won't go amiss.

I would strongly advise against using a Q-tip or any other physical implement to clean the MAF sensor. A lot of people confuse the airflow temperature sensor (AFTS) which is incorporated into the same physical unit with the mass airflow sensor (MAFS). It is not helped by most simply calling the combined unit the mass airflow sensor. The AFTS can easily be seen (looks bulbous and brown in color) as it stands perpendicular to the airflow and can be cleaned with the sensor unit installed. However, the MAFS (two thin wires, to look at) is tucked up inside the unit's body and the aperture for the sensor opens parallel to the airflow. This means that the sensor unit has to be removed from the throttle body to actually see it and clean it. For cleaning both the MAF and the AFTS use only proper MAFS cleaning spray. As a bonus, removing the MAFS/AFTS from the throttle body allows for easier cleaning of the throttle plate and the throttle body.

After cleaning the MAFS and particularly the throttle body, disconnect the 12 V battery for 5-15 seconds then reconnect. This will cause the ECM to reinitialize and relearn the idle position for the throttle plate. If you don't do this you may get rough running at idle or even a failure for the engine to start, depending on how bad the throttle plate/body and MAFS were.

This thread: P0171 contains good information about cleaning the MAF sensor. A good photo of the MAF part in post #8

 

I found on both my gen2 a good dosing of Redex improved performance.

 

Just the plugs were replaced, and p0301 persists? Try swapping cyl 1 and 4 ignition coils; see if the code changes, to p0304. If no change, I’d suspect failing head gasket: boroscope inspection and/or leak down test would be the way to check for that.