DVC does not report your ownership to the reportig agencies, so it certainly won't harm anything. In general, timeshares are difficult to value from a net worth standpoint so many feel they could hurt credit standing especially if there is a mortgage involved. I don't see any downside if nothing is owed on the property and/or if you can establish a value for the property.
No. If you finance with Disney, the loan will not appear on any of your credit reports. So it will not hurt your credit in that way.
Yes. If you apply for credit(loan) elsewhere while you are in the middle of a Disney loan, applications will ask if you have any outstanding depts and the amount of your monthly payments. If ou answer honestly it may hurt your chances of getting approved.