The limits being talked about ($500 for values, $1K for mods, $1.5K for deluxes) are not automatic limits, they are UPPER limits. You can set your room charge at any amount up to or equal to the limit for your level of resort.
When I stayed at CBR last year, I could have had a $1K limit but I requested my room charge set at $500. Tomorrow, I'll be checking into POFQ, another mod, and setting my limit around $750 or $800 or so.
And by the way, you don't need a credit card to set up a room charge. Debit card, cash, Disney Dollars, they all work for setting up a room charge.
And if you're using ANY type of card, WDW absolutely, definitely just puts it through as one big charge once you reach your limit or check out, whichever comes first. For me, it was great to have one $500 charge on my bank statement rather than 47 individual little charges. Each time you make a room charge purchase you will get a receipt. You can go to your resort's Guest Services Desk and get an up-to-the-minute printout of your itemized room charge activity at any time.
When I met my limit last year, my room charge was declined. I've read that others had the experience that the computer must have automatically opened up a second room charge because they went over their limit but were never declined. Tomorrow, I'll request at POFQ that my room charge NOT be automatically renewed, that my card be declined instead. It's my daffy little way of controlling my spending.
Last year, with my wife and our 5 year old and 2.5 year old (at the time), it took us from Sunday afternoon until Friday afternoon to reach the $500 mark. We ate mostly counter-service, plus had already pre-paid for one dinner (Hoop). Plus we had about $200 in Disney Dollars for the kids.