That's actually near impossible each EU country will have a flat VAT rate as well as reduced VAT rates on certain items (books, children cloths, cat sex toys etc.) there are also other different regulations especially in regards to 2nd hand items and crafted items.

In some EU countries re-selling an item will not trigger VAT, in some it will, in some it might require some work to be done (e.g. refurbishing) in which case you need to charge VAT but even that's not that simple because in some countries you only charge VAT on the actual work and bill of material that went into the refurbishing process, in some countries you need to charge VAT for the whole amount based on the final sale price and the list goes on and on and on.

VAT MOSS also completely ignores the fact that you might be VAT exempt in your own country, if you are in the UK you can choose not to register for VAT if your business earns under 100K a year in this case you simply do not charge VAT, but well Spain doesn't care about that so they might come knocking because you have a Spanish costumer or 2.

There is no realistic way for people to figure out when and how much VAT you'll need to charge, and you'll need quite a good and expensive accountant to sort that out and even they might actually not know everything.