If the words are random, then it will be much more difficult to memorize, and the chances will be greater that you will lose access to your funds.
[snip]
The above steps would make it much more difficult for a brainwallet farmer to try to crack my brainwallet because of the exponentially greater number of potential passphrases if you use two sentences found in literature or are otherwise easily crackable.
It should also be noted that I am not going to personally endorse this strategy of creating a brain wallet, and as a result I am not going to take responsibility if anyone were to have their funds stolen as a result of employing this kind of strategy.
if someone can find any non-trival errors in my math then please feel free to point them out
As to math problems, I'll only point out that there are nowhere near 1 million english words - there are less than 200k words in total. If these are words are to be memorized, they must be known to the user. A more practical number to use here is 10,000. This alone changes your math to a final result of 3.3 years instead of 3.3 trillion years. If the words are not random, then of course this goes way way down.
This may not be good enough and may result in the loss of your funds. Don't do this. If you are unwilling to memorize (and keep memorized) those 12+ RANDOM words, then don't use a brainwallet. Nobody said you have to memorize them into one long list - feel free to make them into four three-word phrases. The KEY is that they have to be ACTUALLY RANDOM. No phrases, no book quotes, no birthdays, etc. Random words, chosen by dice roll or other non-computer-generated method.
You can also use a hybrid approach. Memorize some of the words, and keep the rest written down somewhere safe. Just nowhere digital.