Welcome aboard Crsavage1.
The newer 4 strokes are fine. In my mind the 2.1 L Merc 115 is the best option. Its the least expensive, the simplest and the lightest. At around 360 lbs it's the lightest 115 on the market. These boats are really nimble when not weighted down. I think just about all 115s are 400lbs, +or - 20 lbs. The 90's like the Etec (2-s) or the Suzuki 4-s are very light at 330 and 345 respectively and excellent choices.
1. You're not crazy. Yet. Your quest for an old Seacreaft is reasonable - even noble. Pretty lines, solid pedigree, and fantastic ride. Based on your automotive rebuilds and the console you built, clearly have all the requisite skills, and aptitude to learn what you need to.
2. You're right the prices are all over the board. you may find an abandoned gem for $500 or someone may be trying to recoup their $8,500 of time and materials on hull with no motor or trailer. Think about what your willing to spend. $2000 for a decent hull is fairly common. A bargain, really... add a used trailer and older running motor and your easily in $4-5K to start.
3. No, you're not nuts. Yet... You've rebuilt old cars for the appreciation of what they are and you've already dipped your mitts in to the toxic resins to craft your own console design. You can do it.
4. Next size up, the 23' - is a much bigger boat. unleas you have a farm, the boat on trailer is unlikely to fit comfortably in your garage.
Stick with the 20' but even though youve already constructed your console, look at the possibility of the Bowrider 19, the Sceptre 20 and Seafari 20, especially since you live up north and going family rec style. The Seafari cuddy is great for sudden bad weather, colder days, sun and wind aversion, drying off and changing, camping, and a place to hide when you're in the doghouse. The Bowrider though few and far between is a great design and both fishing and family friendly. probably pretty nice for duck hunting, too! the Sceptre's a great little family runabout and probably the best of the lot for water toys. I would probably avoid the bracket.
One more thing to think about
: Try to plan your boat and buy parts, etc., a step at a time. Avoid the temptation to stock up on deals and things you might need on ebay or craigslist, until you really need them. It's really easy to fill a shed with future plans
When you find yourself doing that, you will be nuts and beyond help
Cheers, and good luck with the search.
P.S., I found my 21 just north of Toledo and have recently seen Seacrafts in Indy, & Covington KY. Also Milwaukee 20 , & Traverse City MI 20 and 23 in the last week. Lots of big water around you, that's good.