X2 with Mac. You could be setting yourself up for some adhesion issues at minimum. From a resale perspective you'll pretty much be the last owner or at least the last one that knows anything about boats if you use automotive paint. Most boats painted like this have issues with the finish within a couple years.
I realize this is an older boat that you're most likely pulling this one back from the brink but I would seriously consider going with gelcoat or at least finding out what the cost difference would be to do it right. You've already done the hard work of the 80/20 (80% prep, 20% spray/buff) rule of refinishing. See if the cost difference of going with gel is a possibility.
As far as flake goes..... I'll bet it's going to cost a significant premium for the materials and if you scratch it matching the repair will be more difficult. It would look great though.