Do I need to pay anything up front?

No.

Upon plan creation your first installment is charged immediately (for some purchases this may be later if your goods are being shipped on a future date). 

Future monthly installments are automatically charged each month on the anniversary of your first payment. This date cannot be changed. Monthly installments show as 'charged' or 'posted' on your account.

In addition to your monthly installment payments there is also an Authorization to guarantee your purchase. An authorization for the full purchase amount is put on hold/reserved upon plan creation. This is not a charge.

• For most plans the authorization will disappear within 30 days or less of your purchase. 
• For some plans the authorization will be periodically re-authorized (at lower amounts as you make installment payments) until your plan is complete. 
• The length of these authorizations is determined by your bank or credit card provider, so contact your financial institution directly for questions.

These authorizations temporarily reduce the amount of credit available, but again, are not a charge, and are required to guarantee your full purchase amount.