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I'm having a problem understanding how to create secure and randomized private keys for paper wallets. Let me explain what I understand so far and then you can let me know if I'm misunderstanding something...
 
When your private key has been imported into the client and it becomes a digital wallet, you can choose to encrypt it by choosing a pass phrase. This pass phrase protects your digital wallet in case it's ever stolen from your computer by a person or malware/viruses, etc...
 
You can turn this same digital wallet into a paper wallet by dumping the private key. You then write down your address and key and hide it somewhere safe. Rather than reusing the same private key though, the best way to do this would be to create a new paper wallet off-line, preferably on a boot CD of Ubuntu and then transfer your coins to the new address.
 
If this is all correct so far, let me explain my problem in more detail. What I need to do right now is create a bunch of brand new private keys and addresses so I can make paper wallets out of them. I encountered 3 problems though, which I detail below.

1. It's been said not to trust random private key generators because they're not random enough and can be figured out by hackers, putting your newly created keys at risk. After hearing about this, I went searching for another way to create secure private keys. I then found out about http://brainwallet.org/. Using that website, rather than using the random key generator, I can enter in my own pass phrase, which will convert what I wrote into a new private key that I could then use. User input makes the resulting private key more unique than anything the random key generator algorithm could come up with by itself.

2. This is where I ran into the second problem. It seems that when people make brain wallets, they use easy to figure out pass phrases. They use lines from books or movies, or anything simple. Hackers then try out different pass phrases until they find one that leads to a private key that has money in it, which they then steal.
 
3. So I don't want to use a random key generator and I don't want to use a simple pass phrase on brainwallet.org to create my own unique key. This gave me the idea of entering in a bunch of gibberish as the pass phrase, for example: fgjDLKJH*gu48;p(guiMmp;r,/;)$%I^)WP$^?)_-[.-HKED)HPvre,/ptrkp Using brainwallet.org, all that gibberish would then be converted into a unique private key which I could then use. It would be much harder for hackers to figure out that pass phrase than something like "The dog jumped over the moon". But then I found out that even typing a bunch of keys is not TRULY random, since there can be some minor repetition. It might take hackers longer to figure out, but it's possible they could.
 
So my problem is, how do I create a TRULY randomized pass phrase to be used on brainwallet.org, so that it will create a TRULY randomized private key that nobody can ever figure out? I've heard about something called Diceware, but I haven't looked into it yet. Is that an acceptable method or is there something better out there I can use?

Thanks for any help!

Let's say you have a ridiculous amount of Bitcoins (Like 30-40,000) that you've been keeping on an exchange and you finally made the decision to send them to your local wallet to secure them. Let's assume a couple things first...

1. You made no errors.
2. You sent all your coins to the correct address.
3. You sent all of them at the same time instead of splitting them up into smaller increments.

Assuming the above, is it at all possible for any of your Bitcoins to be lost in between the sending address and the receiving address? The Bitcoins wouldn't show up at the receiving address and you wouldn't have the ability to send them again. They've just vanished never to be seen again, like the client made an error that can't be undone. Is this possible? I guess what I'm asking is if the system is designed to make something like this impossible from happening with any size transaction.