Good news on the outing with your Dad, some solid info from along time member there - every one of those outings is worth a hundred solo trips..
As for your initial question - hitting the big lake in an 18 ftr, its not a problem, so long as you are willing to invest a little time to learn what the water conditions will be like based on the available information -- and respect the resource I hit both big lakes regularly with my 18ftr. The internet has a ton of info. I like Windfinder personally. It misses once in a while, but not often. Learn what wind speeds and directions on your forecast site mean on the lake. And if you are going out on a day when a couple Ks change in the wind makes a difference to your safety - ask yourself why? If I have a west wind at 5k, and it doubles, or even triples, depending on where I am I know I don't have to worry. If it says 25k, there's other things to do with my life. I also have a VHF, and at this time of year when the heat and humidity can drive storm cells up from nowhere in a flash I am listening to the weather channel, the anglers, and watching the lake and skys for signs I gotta get off. I have been chased off a couple times, so far, so good, an nothing serious or even white knuckle worthy. Just time to go.Have I pulled off for nothing more than once. Yup. But you only get one chance to do it too late. Don't play games with the water - a fish ain't worth it. There are incredible fishing opportunities on the big lakes you can't get anywhere else around here. Just respect the winds, waves and water.
If you are interested in Erie at this end, spend some time on the long point forum, or there are a few facebook pages that are pretty easily discovered
or, send me a PM, and I'll take you out one day and we can chat.