Not much to estimating/calculating if you have the material dimensions - and you do. It can even be done without a tape measure - lay a piece of wood equal in thickness to your desired gap (a quarter-inch or more), the flooring on top of that, then the transition piece on top of that and mark the bottom of the door on the hinge side, then the other side. That's how much should be cut off the door. This is all far easier than you are making it out to be. All you need to do is find a carpenter/handy person and ask them to give you an estimate to cut 4 doors. Get more than one estimate, if you don't like what you hear.