Hi Abibi83,
Re: your questions:
1) MT4 doesn't inherently support multi-currency back-tests. For one you can't place trades for two different currencies in the same back-test. Of course, given Metatrader's widespread usage, it may be that someone has found a suitable workaround for what you are trying to test. I would suggest doing a few searches.
2) You can find out the available date ranges for each instrument here:
http://tickstory.com/dukascopy-historic ... te-ranges/. The amount of data you can test in MT4 is limited, though - if your FXT files are greater than 4GB, you could run into troubles. That said, some users have reported using up to 5 years of historical data with no issues.
Hope this helps & hope you join us!