Hey Neild, I think it is the right idea to use your business domain as the e-mail address. It gives a professional look to your site and gains the trust of your buyers. If you do add a new e-mail address to your PayPal account. Then you should update it also on the Administration page on your website. This way the e-mail address given to your buyers matches the e-mail address on your PayPal account.
In relation to logging into your account. The primary e-mail address on your PayPal account will always be the log-in/username. Though an e-mail address may not be primary, once it has been confirmed and is still active on your account. Then you can still receive funds to it from eBay sales. Although I would suggest that for convenience sake, you keep your business account and personal account separate. Hop that helps.
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