I think you can pay your bill in cash before you leave. I've never had a balance, but I know that we bought tickets for the waterpark at the BC, and the CM couldn't figure out how to do it without charging it to our room (DH wanted to pay cash, but wanted the tickets on our KTTWC.

They charged it to the room, then he was able to immediately pay cash toward it. I assume it would be the same way for other things.
We are a cash family, too. But I think that figure seems high. Like I said, we always come home with extra money, and DH reminded me that we brought about 200 a day in May because we were doing the cruise as well, and used it for Nassau. It was way too much money!
I would use the dining credits for Artist Point; you would probably get the best value here. Of course that's depending on what you want to order. What kind of dining plan is it?
I am planning a GG trip right now, with people who have never been. I have been doing a lot of number crunching (my dad wants to pay for the trip for all of us).
The categories I have for spending (we will do the tickets and hotel as a package, but family was unconvinced on the
DDP) are:
1. Meals
I have figured $35/meal/adult at TS (sit-down) restaurants, and $15 per child. This is averaging TS, Buffets, lunches and dinners, so it might vary. Counter services I have averaged to $17/adult and $10/child. Snacks I have figures at about $10/day (It was $8, but I rounded it up. We are bringing our own water - or actually having it delivered to the hotel). i also added in one "Signature" meal, $76/adult and $24/child. Don't forget to factor in tips for sit-down meals. You can figure that by using the above numbers and factoring in 20% (again, just to be over prepared).
The dining plan works out better, so we will go with that. And as a side note, I included an appetizer or dessert with most meals, so your price may be lower. I'm like you; I'd rather be over prepared. I thought the numbers might help.
2. Souvenirs: I don't know what your spending habits are, but my DH is frugal; he will buy 1-2 T-shirts and be good. DS earns his own money throughout the year for vacation spending money and we usually buy him 1-2 t-shirts with maybe an occasional "big" item (Legos

). I am the big spender! Last year I came home with 4 5 T-shirts (I was told we weren't going back to WDW!) 2 ornaments, a scrapbook kit, crystal, etc. We still had almost $400 left over (again, that was estimating $200/day, with a cruise).
My most expensive top was $36.
3. Entertainment: Mini Golf? Renting a surrey bike? There's so much to do at Disney, this isn't a necessity, but you can find prices and plan accordingly.
4. Traveling expenses. Are you factoring in food at airports, gas for the car, a car rental? (I don't know that you can pay cash) You will need money for that!
5. Other? Are you hiring a sitter? Renting strollers?
I think that covers it, in a condensed format.

Well, as condensed as I could get it. It's hard to tell how much you will need - so much depends on your spending habits. $100/day always covered our snacks, souvenirs, tips and travel with money to spare. But that was on DxDP, and we had 2 snacks/day covered. Plus, consider we aren't big drinkers. Alcohol adds to the cost of a Disney Vacation (both before and the morning after

) Also, the years we did F&WF, I had a $100 Gift card dedicated to that. And I added more to it! Did I say we weren't big drinkers...
Again, hope that helps in planning. Take what will make you comfortable - don't stress about it. But please don't take any more that you can stand to lose. Your debit card should be good at WDW, and get travelers checks. Plus divide the cash between the carry on luggage, purses, etc after you pass security. You don't want to lose anything and be out 3 grand!