Legally there is no limit.
You should bring at least £15 since Europe have some really cool things especialy the UK!
France
That depends where you are buying it. Not only which country but which outlet.
It is much easier to name which countries are found in Europe. This way, if a country is not on the list then you know it is not located in Europe. A link is provided below with the list of countries in Europe, either fully or partially.
enough money
Much of Europe
The Alps.
That's something you would have to check with customs because of the statutes in terms of what you can and cannot bring into the country over the border. If you are a legal US resident, it also depends on how long you have been out of the country.
depends which country, i live in Ireland and its pretty expensive, average wage of the ppl i know is 30,000 euro per year (newly qualified nurse, teacher, average bank worker). eastern Europe is a lot cheaper. a pint of beer is just under 5 euro in dublin.
if your talking about ww1, then alliances between country's
It varied according to the laws of the receiving country.