How are the puppies sold ? Can I buy at once or is there some type of payment plan?

They have a few options. You can pay in full and bring the puppy home immediately. They have a 2 week layaway for a (25%?) Down payment. They also have a financing option that I'm slightly unfamiliar with but you can make very small first payment and bring puppy home immediately.

They have payment plans

You can do both but they use an agency for credit