Hi,
The "registration not allowed" message is because you have the "new account creation" setting of the Joomla user manager turned off so HikaShop abids by that setting and doesn't display the registration form.
Regarding the "no shipping method found" message, that's because the shipping plugin needs the user address to be able to get the shipping fees and you didn't enter your address yet at that point so it can't find any shipping fees and display that message.
That depends on how your checkout is configured. You could for example slipt your checkout is two steps with the registration/address on the first step and the rest on the second step. That way, when reaching the second step, your customers would have an address and the shipping methods would display properly.