Most on here are bigger experts than I, but I'll take a stab:
Cheapest time: Value seasons (e.g., September). I typically consult the "my first visit to Disney World" website (just Google it) for a run-down of annual pricing seasons and a listing of the cheapest weeks.
Best Value: The newest are the Art of Animation (Little Mermaid rooms are standard; the rest is expensive family suites) and Pop Century. I'd go for the latter, for cheaper prices and less of a walk to the bus (Little Mermaid Rooms at AoA are far from the depot).
Day to visit each [you said resort - I assume you meant park!??!] - In general, avoid MK on weekends and Monday (b/c most people begin and end their vacation there), and Epcot's World Showcase on weekends (during festivals) and AK on Sundays. Also, avoid the park with morning extra magic hours in the morning (unless you have parkhoppers -- then visit if you wish for a couple of hours and hop somewhere else) and the park with evening extra magic hours in the evening (again, unless you want to hop there for extra magic hours from another park). This is because the extra magic hours attract a crowd swell of resort guests. If you don't have parkhoppers, visit the EMH parks the day after their EMH, when the resort guests will have moved on to the other parks. All that being said, crowds of any size can be largely overcome with a good touring plan, so don't let a park's being "non-recommended" for a particular day dissuade you if that's where you want to go.
Money-saving tips: They vary, but for us it's traveling during the off-season when everything is cheaper, and using a rewards credit card that accrues points and saves us about $600 on airfare every time we fly down to Orlando.
Deals: Keep an eye on the "Special Offers" section of the official WDW website, where seasonal deals are displayed. Even if you have a vacation booked, you can have discounts applied later if one comes up for your dates/resort/situation. Just call WDW and modify your reservation to include the discount, but do it quickly, because availability is always limited and it's first-come, first served.
What Not To Do: Do not underplan. (It doesn't look like you're in any danger of this, OP.) Do your homework, and start booking and planning your visit well over 6 months ahead of time (180 days from your arrival is when you can made dining reservations if staying onsite), including making dining and Fastpass+ reservations as soon as they are available, so all your ducks are in a row by the time you travel. "Winging it" is great for frequent visitors, but not for the uninitiated. You can always deviate from the plan if circumstances dictate, but having a good plan in the first place, and being able to set realistic expectations based on foreknowledge of the parks, touring strategies and the new MyMagic+ systems ensures the greatest chance of an amazing time. (My second bit of advice, and it's fairly personal and subjective, is: arrive at your chosen park at rope drop and tour for 4-5 hours, but don't try to go all day. Plan a 3-4 hour nap break after lunch every single day, when the crowds and heat are at their most oppressive. Go back to your hotel, swim, take a nap in the air-conditioned room, grab a shower, or just relax and watch TV. You'll be amazed at how rejuvenated you feel. With adequate rest, you'll get as much done in two 4-5 hour stints in the parks as you would have if you'd stayed from opening 'til close, and you'll be happy instead of exhausted.)
Cost: For my family of four, this is the typical cost breakdown for a week:
1 - Airfare from Syracuse NY to Orlando via JetBlue: $1,200 ($300 per person; we only pay about $600 because of our rewards points, however)
2 - Moderate WDW Hotel, standard room, 6 nights: $1,200 (with seasonal discount offer of 20% off)
3 - 7-day park hopper tickets (2 adult, 2 child): $1,450
4 - Food (2014 Disney Dining Plan or equivalent out-of-pocket, with 1 counter service meal, 1 table service meal and 1 snack per person, per day): $900.
Grand total: $4750 (without the airfare discount). We don't budget anything extra for souvenirs (kids bring and use birthday or allowance money if they want), in-park food (we bring our own breakfast items and eat it in the hotel room) or transportation (we rely exclusively on WDW transportation - no rental cars or taxis).
