Clicking through our Reseller link simply tells Authorize.Net to pay us a commission for referring you to them, whereas we get nothing from Authorize.Net if you go directly to their site to enroll, so of course we'd prefer that you follow our link, but that's really the only difference. :^)
A 'merchant account' is just a special type of bank account that allows you to accept credit card payments directly into that account. This is unrelated to our being a Reseller and Partner with Authorize.Net, and unrelated to any other accounts you may maintain with other services for other reasons, such as a PayPal account or your E-junkie account. Your choice of merchant account provider is your choice; as long as they can work with Authorize.Net, it's entirely up to you.
You should not require your own secure server, nor an SSL certificate for your domain, nor PCI compliance, because you are using E-junkie as a "hosted" e-commerce provider which is already secure and PCI compliant, and we can provide our most recent PCI compliance report upon request via email. You would only need your own secure server, SSL encryption certificate and PCI compliance auditing if you were using "licensed" e-commerce software that gets installed on your own server to run there on its own, which is not the case with E-junkie.
While the buyer is using our cart service to shop for items on your site, the order they build in their cart is completely anonymous, as no personal, financial nor other sensitive data is being exchanged at that point. When the buyer proceeds to checkout to pay with a credit card that will be processed using your Authorize.Net service, they are taken to a secure checkout page that we generate for you on our server, and we handle transmitting their private/financial data to Authorize.Net via a secure channel for you.