1)if after that i use my B2 with 3DS in order to use dream radar, will B2 be treated as one with 3DS and so i will lose my FC??
No, since you don't go online, in fact, you can just send the Pokemon and Items from DR to you game in the 3DS, and get them in your game in your DSi since Unova Link never interacts directly with DR. DR is a Face Riders like game, after you finish your session you send the Pokémon and Items data to your BW2 game WITHOUT loading the BW2 save.
2)what if i just play the game (NOT wifi play) in other system? will also lose FC? Do i also lose global link settings in any occassion?
Playing the game in another system but not going WiFi will not update (change) your FC, nor delete you friend roster but it still has a penalty, all daily based events get "frozen" for 24/48 hours starting the moment you intentionally save your game in the non main system, also, you will be locked out of DW for the same amount of time.
And no, you don't lose you DW settings.
3DS FC Ares 3738 0446 1787 <> Black FC Ares 0389 8392 9652 Dream World Collection: http://tinyurl.com/3qz7odk