Hi,
1. You already had to sell your digital products with a VAT rate depending on the country of the customer since 2015 with the MOSS.
This new legislation basically means that you now have to do the same with physical products.
Now, I can't say there are no differences. Because you have many different rules for different types of products for different countries. Then the rates won't necessarily be the same. For example, in France we have several reduced VAT rates instead of 20% for some food products ( 10% or 5.5% based on the type of food ), but there are also special rules for shipping to some remote places like Guyane with VAT rates at 2.1% or 8.5%... So in fact, it's still a big mess
The best is to talk to your local tax office to check with them what you should be doing based on what products you sell where.
2. It's based on the website domain. So regardless of whether you have HikaMarket or not, you'll only pay 50€ once per website.