My advice, get the 5/3/1 2nd edition ebook. I find it's layout and the way it's written way mroe simple and easy to follow. 531 for powerlifting is an expansion of the program and b Beyond 531 really assumes you already know the program.
I can't stress this enough:
GET AND READ THE 2ND EDITION E BOOK. READ IT 10 TIMES.
Getting 12 on 3+ week isn't that crazy, getting 5 on the 1+ week is incredibly common. If you try to progress "faster" than the program, especially without a coach it will catch up to you quick, your form will fail and you'll go nowhere. Honestly don't even worry about anything in the beyond book yet, you are so new to training basic 531 will get you to some serious places.
Just do 531; Triumvirate or BBB, start with 90% and work hard. I wish someone slapped me in the face and told me this when I started.
And yes your lifts are out of whack strength wise with your upper body being stronger relatively but if you follow the program and up 2.5kg's on upper and 5kgs on lower the lower lifts will go past them soon enough.