But what will happen to any sites or payments that people try make to the previous email I had used? Do they still go through or is it better to make a new paypal account?
Well, if the email address is linked to your account, new or old, you will still get paid. Like TND said, you can add up to eight email address to your account. Thus you do not need to create a new paypal account because you change email address. Just add the new one then remove the old one if it is no longer valid. You can only have 1 Personal Paypal account + 1 Premier/Business account only.
Its super easy and you dont even have to wait. You just put the new one in there and switch with the main email.
No, it does not matter which email address is the primary one as far as receiving payments from. But I believe that the primary email address is useful only when Paypal needs to contact you about some alerts or something as it would go to that account. Notifications of payment will go to the email address which payment is sent to.