Hi HM Lover, I dont know how much flexibility you have with your Disney days but if you can visit midweek thatd be best; it can get crazy busy on the weekends.
Next Aprils dates cant be booked yet (they go up to March 3 right now), but you can see on their site some initial planning info; note that if you do want to try and stay at the resort Id recommend making a preemptive booking online once they open up the dates; you can always cancel it later (up until a few weeks before arrival). And they fill up QUICKLY, so dont delay if interested.
For planning purposes lets say youll be visiting during a Value period.
Best case for a room sleeping 4 is starting around USD $400 per night at the
Disneyland Hotel (
http://www.disneyhotels.jp/english/reserve/tdh_price_e.html), $450 at the Ambassador (
http://www.disneyhotels.jp/english/reserve/tdh_price_e.html), and $500 per night at Mira Costa (
http://www.disneyhotels.jp/english/reserve/dhm_price_e.html).
For comparison, the nearby Sheraton Grande Tokyo Bay is offering a room sleeping 4, checking in April 5 and checking out April 8, for around $220 a night.
If you stay at one of the resort hotels you can get their version of a park hopper pass good any day of your visit (otherwise the public tickets only have the park hopper kick in on the 3rd and 4th days). Ticket pricing for hotel guests is at
http://www.disneyhotels.jp/english/guest_benefits/index.html figure about $160 for each adult, and $100-$140 for each kid based on their age, for a 3-day ticket. (Public pricing is at
http://www.tokyodisneyresort.jp/en/ticket/multipass/index.html; youre able to get these instead if you dont care about the park hopper feature for the first 2 days.)
For dining at the parks, this site has some really good info on the types of things available and the prices
http://konnichiwamickey.wordpress.com/category/chow-time/. You can use that to help estimate food costs. One thing to keep in mind is portions are typically smaller than wed run into in the US.
Hope this is helpful. Please post back with ANY questions you have!