Cal here from Shopify, thanks for reaching out to us. How are you keeping today?
This is a great question, and I would suggest using one of our approved Payment Gateways for your region. You can find a comprehensive list of those gateways here. I would never recommend using someone else's account as your payment gateway, regardless of Paypal's policy on this.
How has the store setup gone? Have you encountered any other difficulties? When are you hoping to launch?