Yeah, skipping a few of the early break points gets you ahead of a large chunk of the riders. Generally speaking, the faster the riders are going, the more likely they are to have at least some bike handling skills and knowledge about how to ride in a group. I would be very careful about trying to just draft in large groups you don't know. The large disorganized packs are where one wrong move will cause a chain reaction that can take down a lot of riders. If I am not riding with friends I know, I generally try to find 2-4 people riding my pace and work together with them. Smaller groups are easier to deal with and you can keep an eye on the riders around you easier to spot anybody who might be too erratic to ride with.
Most of all, just try to enjoy the ride. So many people get their heads down and ride hard and get so wrapped up in "getting there" that they miss the beauty of the scenery and all the people cheering you on along the way. The most touching part of the ride is when you see a group of 1-4 people standing at the end of a driveway out in the country somewhere with cowbells or a big sign, hollering encouragement towards the riders. You can tell that they have some personal connection to the cause and it just makes a little bit of the tiredness evaporate out of your legs each time you pedal past them, knowing that there are thousands of people out there riding to help them or their loved one.
As far as how to find a group to ride with, the ready2roll training series is great for that, because they start in waves by speed at their training rides, and you will eventually find yourself riding with a lot of the same people week after week. It is easy to talk to a few of them and find out when and where they plan to start the MS150 and arrange to meet up and ride together. You can do the same with some of the recommended rides from the MS Society, but you aren't guaranteed to see the same people and same pace groups at each ride.