A 4-day base ticket in mid-January will run you somewhere in the $430 to $456 range depending on start date. That ticket is good for any 4 days within a 7-day window.
A 10-day base ticket at that same time will run you $501 to $547, and is good any 10 days within a 14-day window. You would not have to use all 10 days, but I'm sharing this as comparison with the next option.
A 4-day base "flexible date" ticket will be $602.79 but would allow use of that 4-day ticket within a full 14-day window. This would cost
more than a base 10-day ticket, and has the same use window.
As
@Robo mentions above, adding the park hopper plus option extends the "use window" an extra day, so a 4-day ticket has 8 days to use it instead of just 7, and gives you access to the waterparks, mini golf and maybe a couple other extras. That option costs an extra $100. If you plan to visit the waterparks, it may be a good deal, but just to extend your ticket by a day - kind of pricey unless you wanted the park hopper anyway (+$80, so the "plus" is only $20 more).
As
@siren0119 mentions...if you are staying on-site at a WDW resort for the full 2-weeks,
and purchase a package, your ticket length will extend to the length of your package reservation. I don't believe that works with room-only or split-stays.
I, personally, would plan my park days closer together within a 7-day window and buy the regular 4-day ticket. But there are options if you really must spread the days out.
Enjoy your vacation!