Meal plan. Depends on how you eat....
It used to be If you want to do at least 2 character dinings you were definately best getting the premium half board, sometimes the plus full board worked well too.
The standard meal plan offers fantastic value for money if you want to eat at least one meal a day at buffet level.
The plus meal plan is pretty poor half board. However Full board it's pretty good. It is particularly good if you want access to restaurants like Bistro Cafe Remy and Captain Jack's (so at least one sit down meal per a day) or if you find the fast food places too busy and would rather eat at buffet level or above.
Thing to remember the meal plans are based on the number of nights. So full board for 3 nights will give you 3 breakfast and 6 meals, you can use these how you chose during your stay. However if you are wanting a full meal on all 4 of the days, you are already making a gain. This is particularly relevant for one sit down meal a day per a day and the full board plus meal or one buffet meal a day and the full board standard meal plan.
If you plan to eat mostly at Non Disney's (vapianos, McDonalds, planet Hollywood, earl of sandwich etc) no meal plan is best.
I've always found that staying at a disney hotels is worth it for the extra magic Hours. I don't particularly like the shuttle buses so have always stayed at Sequioa Lodge or above but if you arent wrangling a wheelchair you may find shuttle buses ok.
Three nights will give you a taster of the place. Four nights if you are organised about it and up every extra Magic Hours you will feel like you've got most of it done, certainly everything you wanted to do, and a few repeats favourites too.
The only caveat to the above is that balance of on to off site may have changed with the recent introduction of the new paid for fast passes, but I haven't worked that out myself or seen anyone else done it yet.