yes
Yes, as the Euro is the legal tender in Spain and Germany. The notes are exactly the same in both countries. Only the coins look different, and that is only on one side. All Euro notes and coins can be used in all of the 18 Eurozone countries.
the currency of the Republic is the euro, so only euro notes and coins are used
cotton
Very definitely, although it's more difficult to do than in the EU. In the US you might have to go to a large bank that has an overseas department, or use an exchange service such as American Express or Deak. In a few very cosmopolitan cities like New York and Washington, some large stores may be willing to take euro notes for purchases because they have a lot of visitors from the EU, but that's not a common practice.
20 euro note
See the Related Link below for a slew of images of both the euro coins and the euro notes.
The 500 euro... though most shops will not accept the 200 or 500 euro bill
The German Mark is no longer legal currency - since the adoption of the Euro. Your only option is to sell them to a numismatist (collector of coins & notes !)
The peseta was the currency of Spain between 1869 and 2002. Along with the French franc, it was also a de factocurrency used in Andorra (which had no national currency with legal tender.The peseta was replaced by the euro (€) in 1999 on currency exchange boards. Euro coins and notes were introduced in January 2002, and on March 1, 2002, the peseta lost its legal tender status in Spain,
The Euro notes have got symbols that can be easily identified. These symbols are the twelve stars and the bridge. The bridge symbolizes the unity among the countries.
the Euro was introduced in France in 2001 (technically it was distributed from the last months of the year 2000) and had legal value from January 1, 2001. During the year 2001 people could use either the Franc or the Euro, as they wanted. From January 1, 2002, the Euro was the only currency with legal value in France, but you could still bring back your old coins and notes to your bank for an exchange. The exchange rate was 6.55957 francs for one Euro.