A more important, legal, requirement that you have/can prove you will be leaving certain countries upon arrival. If you arrive on a 1 way ticket it could appear to some countries immigration staff that you intend to stay. You might want to purchase a cheap/fully refundable flight/bus/train/boat to another country.

As for your planning you're going to pay one way or another for flexible travel ideas. You may want to look into cheap throwaway tickets that get you to your destination with no intent of using the remainder but cost a lot less than a one way ticket.