When specifically will you be at WDW? Also, have you ever been to WDW before? My response to you may vary depending on your answer to these two questions.
If you go in late April, after the spring break/Easter rush has passed, crowds should return to more moderate levels and the need to stick to a touring and restaurant plan is not as crucial. If you are planning on visiting WDW smack dab during one of the busiest times of the year (early to mid-April) I would highly suggest you have a plan of attack and make some ADR's.
If you have never been to WDW, I would suggest you consider developing a "loose" plan, one that does allow you a bit of flexibility. At least lay out what parks on what days, and if you are going to hop, how are you going to work it. Also, it is important to determine your your must-see and must-do priorities for each park. If you are visiting during a peak time, then I would amp up your plan from loose to more firm.
Finally, if you have not been to WDW before, the best advice I have for you is to study your park maps in advance to get a good idea of the layout of things. If you do not do this, you likely will spend a significant amount of wasted time hovering over your park maps, trying to figure out how to get from point A to point B. We no longer need to use park maps (except for show times), and it saves a ton of time. If you don't need a park map, then your need for a "plan" decreases, IMHO.
If it were me going during spring break (or Thanksgiving, Christmas or the summer), I would have ADR's and a good plan even though I have a decent amount of WDW experience, because it would allow me to maximize my time during the busiest season(s).