1. Am I being really stupid and optimistic to think this way? How much of a chance/risk do you think it is for the price to not go up any higher in 2014? IMO, it almost seems guaranteed the price will at least hit $1200-$1300/btc sometime next year.... or is there a risk that I'm not aware of?
There is one correct answer to this question: "Nobody knows." It's kind of like the stock market, and kind of like the currency exchange market, and nobody knows which direction those will go either.
3. Will I even be able to buy $1mil worth of BTCs? Does it depend on who's selling right at the moment I'm trying to buy some? How does this work?
Yes, it depends on who's selling, but many people on the exchanges have limit orders that will stay around until they are fulfilled or cancelled. When you place on order to buy, the exchange finds the lowest-priced orders that will meet your quantity. This means that when you buy a higher quantity, the price will be higher, because the lower-priced orders are "used up."
4. Will I have to pay taxes on capital gains? I don't wanna pay shit to the US gov, how would they know how much I made off BTCs?
Yes. If the IRS audits you, they can see your bank accounts, which presumably will show money coming in from an exchange.
I'm thinking of putting an automatic sell order right when BTCs hit $1500 in 2014.... is that too high or should I put a lower limit?
See the answer to question number 1.