Hey there! First, what led you to wonder if only using Paypal was a bad idea?
It's simply a payment gateway for your Shopify store, a way for customers to pay you for the order. The only thing you'd want to be concerned about is the transaction fees you'll be paying for each order. However, every payment gateway has transactions fees so you'll just want to compare them to see if it is the best option for you. Here is a list of them by country so you can compare!
Hope that helps, looking forward to hearing back from you.