You generally have to purchase the DDP for all nights and for all guests. I suppose if you wanted to do a split stay, you could do the DDP for only one leg of the stay.
If you have different needs, I would skip the DDP and just use the
DVC discount - assuming you have a blue card, or an AP discount, or a TAbles In Wonderland card. These are much more flexible.
There is no requirement to buy tickets. Although if you do have tickets, you can book fast passes starting 60 days out from your first day of your stay.