If you're going during a popular time or want a room that is really hard to get/sells out early, I'd book as soon as you know you are going. Otherwise, it's really a coin toss.
People who have ressies still get pin codes. I speak from experience on that one. There is no rhyme or reason to how pin codes are distributed, that anyone can figure out at least.
Pin codes, like all discounts, are based on availability. If your existing reservation meets the standards to any discount, you may apply it at any time. The only things you need to look out for is if the cost of your package goes down in the under 45 days time frame, or your room only reservation within 6 days of check-in, you may have to pay a change fee. I *think* that is $50--someone will correct me if I have the amount wrong. If you do anything (upgrade resort, add days, etc) that increases the overall cost, there is no fee. Or rather, it's waived. Paying a $50 fee to lower your costs by $500 (for example) is well worth it though! You'd still come out $450 ahead.