There are two lakes in Lake St. Louis, one is ~ 550 acres and the other is ~ 75 acres. There are limitations on boat length and engine size. I refer you to the Lake St. Louis Community Association rules and regulations document (http://www.lslca.com/docs/BOATING%20RULES%202007%20Revised%205-22-07.doc). The LSLCA website is http://lslca.com. There are no jetskis allowed on either lake.
Engine size on the small lake is 9.9 hp.
Sounds like Lake St. Louis may not accomodate your needs but the Mississippi Riiver is just a few miles away and you can put about anything on it.
Another possibility is Mark Twain Lake, (http://www.marktwainlake.com) about 1.5 hours north and a little west of Lake St Louis. It is an Corps of Engineers lake and will accomodate about anything you want. As a Corps lake, you cannot build on the lake. There are two marina's available but the wait list is about 2 years for a slip. You can, of course, trailor your water craft as you wish. Mark Twain is a very popular weekend home destination for people in this area. It is a very quiet getaway location.
I hope this helps.
Jim