You don't have to create a PayPal account in order to buy from a merchant that uses PayPal for processing their payments. You can use your credit card just like with any other purchase.
Creating a PayPal business account is, as you say, mainly for businesses wanting to accept payments, not make them. PayPal doesn't require you, the customer, to have an account just to make a payment to a merchant. We have dozens of customers a day make purchases through us using our PayPal account (we're small), and for them the main attraction to using PayPal to pay us is that PayPal has pretty good security and offers some very good customer protections against fraud. They don't have to create a PayPal account just to pay us, though.
When you create a PayPal business account, you link a bank account to it that they verify, then they issue you a PayPal MasterCard, which is a debit card that links to your PayPal account. When you make purchases, if the funds are in your PayPal account (because, for instance, you're using PayPal as your merchant processor) then the payment is deducted from that. If there's no money in your PayPal account then PayPal simply debits the bank account you linked with them, no differently than if you were to use your bank's debit card.
In this instance, if you don't plan to use PayPal for merchant processing then there's no real reason to open a business account. It doesn't have any advantages over your bank's debit card and, IMHO, just adds another layer of complexity and paperwork to your accounting for no identifiable benefit.
I hope this helps.