We'll be sailing in the Great Lakes, and I don't see us racing - - just cruising. I will compare the fin to the full keel that I am accustomed to - I've pretty much ruled out the wing
I'll throw in my two cents here ... the only thing you really need to worry about as far as your keel goes, is whether it is in good shape and whether it is atttached to the boat properly. I think that it's probably going to be a while before you are seriously racing, at which time you'll be able to decide whether the prevailing winds in your area favour downwind or upwind performance, which is pretty well the only reason to choose between a fin and a wing.
Look for something in good shape, in your budget, that is comfortable and that you think is beautiful. Some boats are faster than others, some are more comfortable, some are prettier and some have more cachet associated with the name, but they all have their good and bad points.
Look at 25 or 30 boats at least. You need to do this in order to develop an understanding of the market in your area, as it relates to your needs and budget. You can't determine if you're buying the right boat, or if it's in good shape or priced fairly without a lot of others to compare it to.
When you find ones that you are interested in, take a lot of pictures, particularly of things that look like they might be problems or look a little out of place. The biggest benefit this forum can offer you is the experience of thousands of people who have seen just about everything somewhere along the way. Don't be shy about posting your pics here and asking people for their opinions. They enjoy answering questions, indeed, for some it's the whole point of their existence, so you're not bothering them - you are allowing them to feel fulfilled.
Once you have found something you really like, then get the surveyor in.
Also - be very, very wary of brokers. While there are some honest ones out there, the majority of used boat salespeople are about as ethical as their counterparts in the auto industry, and their word is not worth the breath it takes to speak it.
Good Luck !