Laquer is old tech, and pretty much not available any more, as teh solvents are heavily regulated as being bad for the environment. I used to use them for street rods and vintage car restoration (and you can still get them for vintage cars if you can prove you're a shop that specializes in that).
But laquer is really not very good paint. Brittle, labor intensive, and not very durable.
Acrylic Urethane is where it's at, not just in OEM finishes, but in custom paint for street rods and the like. Acrylic enamels are ok as long as they are catalyzed, which essentially turns them into urethane. Cheaper, but not so good for custom finishes.
Clear is merely paint without a pigment. Always use a clear that is the same as the paint that is underneath it, for compatability.