How can I include in my personal watchlist several itens at the same time instead of one by one?
You may try to edit the watchlist file directly. If you have added any item in watchlist then you can go to "%appdata%\Lunetek Software\Stockalyze" folder and edit watchlists.xml file directly. Make sure you have Stockalyze closed and ensure that data is not incorrect and be cautious about that.
I will not recommend this approach unless you wan to do it. :) Nothing wrong will happen, but you should take backup of watchlists.xml if you want to revert back to original in case of any mistake.