Yes, you can. Business Pro、VPS、DDS、DDSPro users have the priviledge to resell the server.
Can I create a web design service for my customers, to design and host their sites here?
Yes, you can.
Can I sell my account per mail address I create ?
Yes, you have complete rights over mail addresses in your account. When problem happens in one of mail address, you will have to become a bridge between our support staff and your customer.
Can I sell my account per domains I have?
Yes, you can. If your customer purchase the domain and you provide the server, the domain's contact information should be your customer and the domain's server information should be your name.