Walk then run
I'd like to add a few things to the excellent comments others have made here with regard to cruising the lake shoreline. I would definitely take a few short overnight cruises before heading out on the "big one". Comments about approaching a strange harbor at night are right on. Waukegan itself is a great example. Stay offshore a few miles one evening and then see how long it takes you to find the (familiar) harbor entrance lights heading back against the light clutter on shore. Now imagine what that would be like if you never saw the harbor entrance before. As to speed in a 27 footer, when I first sailed this area in a similar sized boat I got a quick appreciation for the scale of things and that many factors influence how many miles you can put under your keel in a day. Lack of wind early and late in the day is to be expected. SW wind prevails much of the summer so keep that in mind. Bashing into steep short waves when they occur during/after storms can be tiring and really slows a smaller boat you down unless the wind is there to help you. In any case a good reliable engine is a must. Hope to see you on the water (in 6 months or so).