This is my first Battlefield game too... Would I be able to join the BF3 division as well as the MW3 one on PS3?

Well you can only be in one squad. But you can practice with the both.

Okay, cool

Welcome to the BF3 world

Unfortanatly you may only be in one squad per time however you can still play with others and attend thier practises etc.)

I see your from EU so feel free to play us warlords or come to our practises at 5pm Wedneday and 4pm Saturday GMT

See you on the Battlefield!