I live in Michigan and love diving the Great Lakes. I also dive inland lakes and nearby quarries. The viz really varies - the Great Lakes can have viz as low as 30-40ft or as much as 100ft+ depending on the lake, weather, etc. The diving around here can be pretty cool (~40 degrees F at about 100ft two weeks ago), however I consistantly dive a 5mm wetsuit with 3mm hooded vest. As for equipment, I don't have anything special, wouldn't mind a dry suit though. Just my opinion, but if you want to dive wrecks then you need to try the Great Lakes.
What sort of depths are in the great lakes?