I was out on a jet ski for about on hour with two little ones and the lake wasn't too bad at all...nothing compared to a busy holiday weekend. The boat traffic alone on the 4th of July can sometimes be five times worse than what it was on Memorial Day.
Add wind to that and it can be extremely choppy. The longer you're on Winni, the more you'll realize that if you're going to do a lot of serious boating, you'd be better off with a heavier boat. And something 24' or bigger usually helps too.
Actually I was on the east side of Bear Island and couldn't believe how calm it was. The west side was choppy, but it's usually the other way around due to the winds coming in off the Ossippee Mountains.
Even the kids commented on it...they said there weren't enough waves on that side of the island.
Welcome to the lake!!
And check back often if you have any other questions...the people on this site are a wealth of information.