ABS, BRAKES, and Traction Control lights turned on, then off?

Hello! I purchased my 2012 Prius with 96,000 miles this Monday, and when driving home today (sunny, clear weather) I noticed that three lights had turned on on the dash; the ABS, BRAKES, and Traction Control lights. In addition to this, there is a whirring sound that happens every ~10 seconds or so that I believe to be the brake actuator, though this sound had been happening about this frequently since the test drive Monday.. The brakes themselves seem to be working fine, and the regenerative breaking is still operational.

After a few hours of googling all of the possibilities that it could be, I came back to the car a few hours later only to have a clear dashboard, and no sign of any trouble.

So far, I have...

1. Driven around my apartment's parking lot (Brakes work fine, lights didn't come back on)
2. Tested my 12v Battery via the Vehicle Signal screen (Interesting results here):
   Without the engine running you can see the whirring noise actually making the voltage dip, and with all the lights on, AC on full blast, windows moving, and the whirring happening, I was actually able to get the voltage down to 11.1... Battery needs changing?
   With the engine running the voltage just stays around 14.2, with or without whirring
   
3. Tried pulling codes with an OBDII scanner, but either I don't have the right one (likely) or the system doesn't have the codes anymore since the lights turned off.
   

Suspected culprits are:

1. Low 12v Voltage, which seems to be able to throw some weird codes on Priuses
2. Failing brake booster assembly or brake booster pump assembly, which looks like it might be covered by Toyota via their "ZJB Customer Support Program" if I have the "right" parts that went wrong
3. Some other failure in the braking system?

So my questions:

1. Should I take this car back to the used car dealership? I am still under their 7 day guarantee, so would be able to get my money back/ get a credit towards a different car.
2. Should I try to get this car fixed by Toyota under the ZJB Customer Support Program? Does this seem to be that issue? Or not, since I'm missing the Red Warning Light and beeping mentioned by the program?
   
3. Is there a chance the dealership "pulled a fast one" on me with this car? I bought from a very reputable and decently large dealership so I would be surprised, but is there any chance they knew the brake system was failing before selling the car?
4. Is this car safe to drive for now? I'm definitely going to get this checked out, but would like to know if it is safe to drive to the dealership/mechanics, or if I should hire someone to tow it.

Thank you loads for reading this far, and thank you greatly in advance for any advice you have to offer!

(I have videos of the whirring sound and Vehicle Signal screen, but cannot yet post them as I don't yet meet the requirements.)

 

I think I should still be within the window for getting the replacement; the specifications I've found say either August 31st of this year, or 150,000 miles/ 10 years from first date the car was used. Unless we're thinking of different replacements?

Either way, you seem sure that the issue with the brakes is related to that faulty booster, could it not be a separate issue? I've just read that it really good be a bunch of different things, but that the Brake Booster issue seems to be a common one.

Another thing I discovered while driving is that braking hard causes the lights to go off. I'm in the process of getting the codes off and realize this will be the greatest help, but does this help the diagnosis process any?

When I got the 11.1, it was under decently heavily load (and I now realize that this matters) and only had two bars of charge. Whenever the battery is better charged it hovers around 12.6 at "Ready," and doesn't dip below 12v. Is there still likely a 12v change in my near future?