It's good to have a registered Business entity, but I'd recommend starting your store first. Given the fact that 50% of eCommerce store owners (beginners) never receive a sale, you might not need one.
I don't want to sound demotivating, but I would start doing it right now and care about legal things later when I know I will be doing this seriously.
As for PayPal, you can apply for the business account using the individual account you have.
Open a new discussion here: http://ask.oberlo.com/t/your-store-feedback ;)