Multi channel e-commerce opens up fantastic sales opportunities, but you have to be aware of your tax obligations. Seller Dynamics helps you manage and handle your VAT obligations, though we do recommend you seek out specialist VAT consultants to help with the admin and registration.
You might need to be registered in the EU countries if you are selling into them. Each country in the EU has a VAT Threshold level. If you sell more than that threshold, in that country, then you are obliged to register for VAT, and to pay the appropriate tax, to that country.