Buying LV in Europe, which country is best?And what is VAT tax?

I had a few questions on purchasing luxury goods overseas, I’m from Florida US and booked a 12 day trip to London, Scotland, Amsterdam, France and Italy in the end of August. I’ve been eyeing the LV boulogne bag for a while and decided our vacation was a solid reason to make said purchase. My question is of the 5 countries I’m visiting where would be the best to buy luxury goods? Should I use the currency of the country or will a Credit card work? Also what is a VAT tax and is it something I need to inform myself on?