Use what was used before, but make sure it dries sufficiently before letting the laminate make contact with the particle board. Remember...this is contact glue and you have to coat both surfaces, allow to dry some and then bring the two surfaces together. The particle board should not appear dry or have a matte appearance...reapply product if the particle board's porosity sucks up too much of the product. You want a thin film on both surfaces.

Since you have milled the product prior to verifying that it was not cupped, they probably won't take it back. So, place some 1/4" mill stock along the top of the wall attachment cleat and the top of the face frame and attach the top with "L" brackets.

If you want a glossy laminate, go Wilsonart instead of Formica. They have a much more durable finish. Either their Aeon or HD finishes will wear much better. I had an old display of Blackstar that was pretty horribly scratched up. It was where the stone countertop samples landed all the time because it had the best under cabinet lighting for viewing.

I think Joe was just advocating painting the front edge , not the entire top ? Filling/painting the front edge would be easier and cheaper than replacing the whole top for a DIYer , though replacement isn't a terribly complex undertaking. If looking for a cheap and fast fix, the edge repair is way less than replacing all the tops. Replacement may be a good value, but not faster or cheaper for the DIYer.