Two interesting questions.

Mt Gox was not the first exchange, nor the first user selling bitcoin.
I've always wondered whether New Liberty Standard was Satoshi.

I doubt that he would have been involved at all in establishing Mt Gox (other than ensuring people understood code or internet protocol interactions), because the threat of crossed wires and people claiming money fraud would be too great. SN understood well enough to keep his name hidden because of such a threat. Gox was the third exchange, so there would be no need for Satoshi by then. He would no doubt have steered clear of it to avoid excess trouble.

Satoshi would have as a goal to get the currency moving. He sort of failed at this for the first 8 months of bitcoin's existence. My guess is that the first few months he spent debugging code and had that as his primary focus, ensuring the base layers of his protocol and software were fully functioning. After those several months of testing with Hal and Martti, he then moved onto the next point.

Who knows why he left the mined coins from 2009/2010 untouched? It can only be speculation, but remember his motivation -- to create a peer to peer currency. He had to make it look like the new currency was being used, but also not look like an individual couldn't join. He couldn't look like he would hold the majority forever or no one would want to join. He could even have sent those coin off to the void to create the mystery, and drum interest. Perhaps he hid coin behind different riddles and tests to test the resilience of the network. Him mining made it look like there were more users than there were, before the extra nonce tagging him was discovered.

I can imagine him buying bitcoin, as this would help the market move and provide demand. He couldn't do this on his own. He could be a middle man, but to get the currency to succeed, he had to get others to use it, perhaps as a buyer or seller. He couldn't use the bitcoin from his main address, as that would flag him too much. His domain was known and linked to him through his transaction and Hal's posts.

He would have seen the rise of value from less than a tenth of cent to a dollar by the time he disappeared. If he was older, then perhaps he mined to the void as his gift to the world. If he was younger, perhaps he is still saving it for a rainy day. There are numerous explanations as to why he may not have touched those coin: it would identify himself (opening all sorts of trouble), he may be dead (Hal, David), he may not need to (being rich off of other bought coin), or he may have lost the methods to retrieve it.

Whatever his reasoning and methods, it worked. Growing in large part due to the community that surrounded him as well.

If he were alive, it would be interesting to know what his attitudes were today, because people can change.

We all learn. There are plenty of mysteries in blockchain that are yet to be discovered, no doubt, especially if you consider that even the hashes of the word 'hello' and the names of linux system files have revealed coin.

It is the greatest unsolved mystery of our day.

And truth be told, we may never have the answer to it.

An overwritten drive would leave no forensic evidence if his goal were to remain hidden.