Does that work with overlay doors? I can see it wouldn't be a problem with inset hinges
It wouldn't make a difference. It's the mount plates that will go back to back. The only difference is that overlay doors, the plate would be closer to the front edge.
Pre finish boards are fine. But I would steer clear of chipboard. MDF is better but Ply is king. If you were to build the whole unit with melamine surface, then the labour to lay all the laminate would be too much so would make sense to buy. For only shelf surfaces I would lay it myself. A lot of the pre finish melamines are wafer thin unless you spend £££.You should look into pre-finished plywood or veneered chipboard/MDF for the carcasses
Another option you could look at is using a company like Cutwrights for pre finish stuff. I used these a fair bit when I worked in hospitality build.