As stated, your dues will be between 3.15 and 4.00 per point, depending on which resort you purchase at. (OKW is lowest, BWV/VWL are highest, with HH and VB in between.) Dues are annual, Jan thru Dec, and are independent of your use year. Dues for your first year would be pro-rated, so if you purchased at the end of July, you would have 5/12th (Aug-Dec) of your annual dues to pay. You may pay dues in one lump sum annually, or you may pay monthly via a Disney direct draft from your checking/savings account.
Property taxes are included in your dues. Disney estimates the yearly taxes, and collects them, and then makes an adjustment at the end of the year when actual taxes are paid. In the past, Disney has always overestimated taxes, so the adjustment has always been a rebate automatically applied to your next year's dues. (For example, they may have estimated $200 for the year, and collected $200, but only had to pay $180. So the $20 would be credited toward the next year's dues.)
If you buy from Disney, you will have no closing costs so the only thing you would have to pay would be your down payment (if you finance) and your pro-rated dues.
Also remember, that if you itemize on your income taxes, then the portion of the dues that are for property taxes are deductible. Also, if you finance, the finance charges are most likely deductible. (This assumes you have no other finance charges on other properties aside from your main residence. I believe the IRS allows deductions for only one vacation property at a time)
If you purchase resale, you will need to arrange your own financing, and pay the entire sale amount at closing. Also, depending on what type of 'deal' you make with the seller, you will also probably wind up paying all closing costs (assume $500 here), and reimbursement to the seller the dues already paid for the remainder of the year. (You would only pay this if there are still points available for the year. How points are banked or borrowed determines your negotiations for what dues should be paid by whom for which points, etc.)