First, review the contracts you had with eBay and PayPal to ensure that you are not violating any of their policies regarding contacting buyers. If doing so would violate a rule, absolutely do not contact them. It's not worth it.

However, if you can do so, here is my recommendation:

Practice "appreciation marketing." Send them a brief email to thank them for their past business (and remind them who you are and what you sold). Then ... offer them a coupon for your new business. Make it a nice offer, not just 5-10%. Be sure that they know how special they are.

I would then keep them as a separate list from your opt-in list (which has agreed to be contacted more regularly).

Use an email service that allows you to track open-rates and click-throughs. You might consider sending a follow-up to those people who open the email but do not click, and also a follow-up offer to those who actually clicked.

I am available to speak if you're interested in more. Either way, best of luck to you!