No modern keyboards have ghosting.
If you select one input per row (or column) per player input as you have indicated you will not have any problems. The most you can do is 2 players with 6 buttons each, assuming that one side of your decoder has 16 lines. The other inputs, like coins and start, need to share inputs.
Make a list of all your windows trick combinations, like alt-enter, and avoid them.
Bob